Revert "[libcxx][pretty printers] Import gdb module in gdb feature check"

This reverts commit 0c2a454.

This was my mistake. When gdb can find its data directory it'll
import it automatically. If it can't (like when you're using a
version from a build folder) you need to give it the data
directory path.

We're safe to assume gdb is installed for testing purposes
so it'll import it for us.

Author: DavidSpickett

libcxx/utils/libcxx/test/features.py

@@ -171,7 +171,6 @@ def check_gdb(cfg):
   # Using the quit command here means that gdb itself exits, not just
   # the "python <...>" command.
   test_src = """\
-import gdb
 try:
   gdb.Breakpoint(\"main\").commands=\"foo\"
 except AttributeError: