Fix AIX build break.

A recent commit broke AIX build. The thread_local type defined functions
were being considered a weak symbol and hence while creating the binary these
symbols were not visible.

This patch is a fix for the same.

gdb/interps.c

@@ -273,7 +273,6 @@ clear_interpreter_hooks (void)
   deprecated_print_frame_info_listing_hook = 0;
   /*print_frame_more_info_hook = 0; */
   deprecated_query_hook = 0;
-  deprecated_warning_hook = 0;
   deprecated_readline_begin_hook = 0;
   deprecated_readline_hook = 0;
   deprecated_readline_end_hook = 0;