PR gdb/17384: Do not print memory errors in safe_read_memory_integer

PR gdb/17384: Do not print memory errors in safe_read_memory_integer

If accessing memory via safe_read_memory_integer fails, that function
used to print an error message even though callers were perfectly able
to handle (and even expected!) failures.

This patch removes the confusing message by changing the routine to
directly use target_read_memory.

gdb/ChangeLog:

	PR gdb/17384
	* corefile.c (struct captured_read_memory_integer_arguments): Remove.
	(do_captured_read_memory_integer): Remove.
	(safe_read_memory_integer): Use target_read_memory directly instead
	of catching errors in do_captured_read_memory_integer.