CLI put: remove -e shorthand

The letter conflicts with --exclude, which would be much better suited for a shorthand.
Unlike --exclude, --exec is only used up to once, less often, and is shorter.
I didn't directly add -e back as a shorthand for --exclude, as I'm not 100% sure yet if we'd want that.

src/main.rs

@@ -900,7 +900,7 @@ fn put_main(args: Vec<String>) -> Result<(), anyhow::Error> {
     opts.optflag("q", "quiet", "Be quiet, implies --no-progress.");
 
     opts.optflag(
-        "e",
+        "",
         "exec",
         "Treat arguments as a command to run, ensuring it succeeds before committing the item.",
     );