Do not show trait vtables as located in the heap in memory diagram (g…

…oogle#1882)

This diagram is misleading and I often explain that the character data
of string literals resides in the executable's static data, with vtables
working the same.

src/smart-pointers/trait-objects.md

@@ -48,30 +48,30 @@ Memory layout after allocating `pets`:
  Stack                             Heap
 .- - - - - - - - - - - - - -.     .- - - - - - - - - - - - - - - - - - - - - - -.
 :                           :     :                                             :
-:    pets                   :     :                     +----+----+----+----+   :
-:   +-----------+-------+   :     :   +-----+-----+  .->| F  | i  | d  | o  |   :
-:   | ptr       |   o---+---+-----+-->| o o | o o |  |  +----+----+----+----+   :
-:   | len       |     2 |   :     :   +-|-|-+-|-|-+  `---------.                :
-:   | capacity  |     2 |   :     :     | |   | |    data      |                :
-:   +-----------+-------+   :     :     | |   | |   +-------+--|-------+        :
-:                           :     :     | |   | '-->| name  |  o, 4, 4 |        :
-:                           :     :     | |   |     | age   |        5 |        :
-`- - - - - - - - - - - - - -'     :     | |   |     +-------+----------+        :
-                                  :     | |   |                                 :
-                                  :     | |   |      vtable                     :
-                                  :     | |   |     +----------------------+    :
-                                  :     | |   '---->| "<Dog as Pet>::talk" |    :
-                                  :     | |         +----------------------+    :
-                                  :     | |                                     :
-                                  :     | |    data                             :
-                                  :     | |   +-------+-------+                 :
-                                  :     | '-->| lives |     9 |                 :
-                                  :     |     +-------+-------+                 :
-                                  :     |                                       :
-                                  :     |      vtable                           :
-                                  :     |     +----------------------+          :
-                                  :     '---->| "<Cat as Pet>::talk" |          :
-                                  :           +----------------------+          :
+:    "pets: Vec<dyn Pet>"   :     :   "data: Cat"         +----+----+----+----+ :
+:   +-----------+-------+   :     :  +-------+-------+    | F  | i  | d  | o  | :
+:   | ptr       |   o---+---+--.  :  | lives |     9 |    +----+----+----+----+ :
+:   | len       |     2 |   :  |  :  +-------+-------+      ^                   :
+:   | capacity  |     2 |   :  |  :       ^                 |                   :
+:   +-----------+-------+   :  |  :       |                 '-------.           :
+:                           :  |  :       |               data:"Dog"|           :
+:                           :  |  :       |              +-------+--|-------+   :
+`- - - - - - - - - - - - - -'  |  :   +---|-+-----+      | name  |  o, 4, 4 |   :
+                               `--+-->| o o | o o-|----->| age   |        5 |   :
+                                  :   +-|---+-|---+      +-------+----------+   :
+                                  :     |     |                                 :
+                                  `- - -| - - |- - - - - - - - - - - - - - - - -'
+                                        |     |
+                                        |     |                      "Program text"
+                                  .- - -| - - |- - - - - - - - - - - - - - - - -.
+                                  :     |     |       vtable                    :
+                                  :     |     |      +----------------------+   :
+                                  :     |     `----->| "<Dog as Pet>::talk" |   :
+                                  :     |            +----------------------+   :
+                                  :     |             vtable                    :
+                                  :     |            +----------------------+   :
+                                  :     '----------->| "<Cat as Pet>::talk" |   :
+                                  :                  +----------------------+   :
                                   :                                             :
                                   '- - - - - - - - - - - - - - - - - - - - - - -'
 ```