Simplify remove_breakpoint interface

All callers pass mark_uninserted, so there's no need for the 'is'
parameter.

gdb/ChangeLog:
2016-08-10  Pedro Alves  <palves@redhat.com>

	PR gdb/19187
	* breakpoint.c (remove_breakpoint): Remove 'is' parameter and
	always pass mark_uninserted to remove_breakpoint_1.
	(insert_breakpoint_locations, remove_breakpoints)
	(remove_breakpoints_pid, update_global_location_list): Update
	callers.