[GDBSYM] Remove unused gdbsym.c

The GDBSYM config.h option was an attempt at QEMU GDB debugging.  I have
removed the code since it is unused and may confuse people wanting to
use the GDB stub.

src/config.h

@@ -164,6 +164,5 @@
 #undef	BUILD_ID		/* Include a custom build ID string,
 				 * e.g "test-foo" */
 #undef	NULL_TRAP		/* Attempt to catch NULL function calls */
-#undef	DUMP_GDBSYM		/* Dump GDB symbol table information */
 
 /* @END general.h */