remote: Small cleanup in compare_section_command

remote: Small cleanup in compare_section_command

The set_general_process call in compare_sections_command isn't
actually needed.  remote_target::verify_memory and
remote_target::xfer_partial already handle making sure the remote is
pointing at the right process or thread.

Getting this out of the way helps a bit with further elimination of
the remote_state global, because we have to handle the case of a user
invoking the command even if not connect to a remote target.

gdb/ChangeLog:
2018-05-22  Pedro Alves  <palves@redhat.com>

	* remote.c (compare_section_command): Remove set_general_process
	call.