Remove frame_id_eq

This replaces frame_id_eq with operator== and operator!=.  I wrote
this for a version of this series that I later abandoned; but since it
simplifies the code, I left this patch in.

Approved-by: Tom Tomey <tom@tromey.com>

gdb/elfread.c

@@ -946,7 +946,7 @@ elf_gnu_ifunc_resolver_stop (code_breakpoint *b)
 
       if (b_return->thread == thread_id
 	  && b_return->loc->requested_address == prev_pc
-	  && frame_id_eq (b_return->frame_id, prev_frame_id))
+	  && b_return->frame_id == prev_frame_id)
 	break;
     }