Fix compiling of top.c

When I moved my last patch forward, somehow I missed removing
the #endif for the HAVE_LIBMPFR case.

Committed as obvious after a quick build.

gdb/ChangeLog:
	* top.c: Remove the extra #endif which was missed.

gdb/top.c

@@ -1581,7 +1581,6 @@ This GDB was configured as follows:\n\
 "));
 #endif
 
-#endif
 #if HAVE_LIBXXHASH
   gdb_printf (stream, _("\
 	     --with-xxhash\n\