Remove a VEC from record-full.c

Remove a VEC from record-full.c

This replaces a VEC in record-full.c with a std::vector.  This version
of the patch also catches a memory leak in the original code noticed
by Simon.

Tested by the buildbot.

gdb/ChangeLog
2018-06-10  Tom Tromey  <tom@tromey.com>

	* record-full.c (record_full_breakpoint_p): Remove typedef.  Don't
	declare VEC.  Add constructor.
	<in_target_beneath>: Now bool.
	(record_full_breakpoints): Now a std::vector, static.
	(record_full_sync_record_breakpoints)
	(record_full_init_record_breakpoints)
	(record_full_target::insert_breakpoint)
	(record_full_target::remove_breakpoint): Update.  Don't use XNEW.