gdb: remove target_ops::commit_resume implementation in record-{btrace, full}.c

The previous patch made the commit_resume implementations in the record
targets unnecessary, as the remote target's commit_resume implementation
won't commit-resume threads for which it didn't see a resume.  This
patch removes them.

gdb/ChangeLog:

	* record-btrace.c (class record_btrace_target): Remove.
	(record_btrace_target::commit_resume): Remove.
	* record-full.c (class record_full_target): Remove.
	(record_full_target::commit_resume): Remove.

Change-Id: I3a68d3d726fb09d8b7165b4edefc330d27803b27