Build system: Removed unnecessary lines in tools/Makefile.am

Removed the TESTdir and TEST_SCRIPTS entries in tools/Makefile.am.
They are not needed and let `make install` try to install
`run-tests.sh` in the source directory, where it already is, causing
an error.

The problem only occurs when `make install` is run without
`DESTRDIR=...`. Then the installation runs without errors.

tools/Makefile.am

@@ -28,11 +28,6 @@ cpdb_pickle_print_CFLAGS = \
 # Tests ("make test"/"make check")
 # ================================
 
-TESTdir = .
-
-TEST_SCRIPTS = \
-        run-tests.sh
-
 TESTS = \
         run-tests.sh