Remove keywords from target debug printer names

Remove keywords from target debug printer names

I recently checked in a patch that removed the use of the "struct"
keyword in some spots.  Doing this pointed out that the target
delegate code preserves this keyword -- but, with C++, it does not
really need to.  This patch changes make-target-delegates.py to remove
these keywords, and updates target-debug.h to follow.  This pointed
out that there was already one redudancy: both
target_debug_print_struct_inferior_p and target_debug_print_inferior_p
existed.

Tested by rebuilding.

Reviewed-by: Kevin Buettner <kevinb@redhat.com>