use the libiberty crc code

use the libiberty crc code

gdb has a copy of some CRC code that also appears in libiberty.
This patch just removes the local copy.

You may notice that "crc32" returns unsigned long but "xcrc32" returns
unsigned int.  However, this does not matter, because crc32 actually
does all its operations in unsigned int type, and only the return
result is widened.  So, the difference does not matter.

	* remote.c (crc32_table, crc32): Remove.
	(remote_verify_memory): Use xcrc32.