Remove arm_insert_single_step_breakpoint

Remove arm_insert_single_step_breakpoint

This patch is to remove arm_insert_single_step_breakpoint.

gdb:

2016-11-08  Yao Qi  <yao.qi@linaro.org>

	* arm-linux-tdep.c (arm_linux_software_single_step): Don't
	call arm_insert_single_step_breakpoint, call
	insert_single_step_breakpoint instead.
	* arm-tdep.c (arm_insert_single_step_breakpoint): Remove.
	(arm_software_single_step): Don't call
	arm_insert_single_step_breakpoint, call
	insert_single_step_breakpoint instead.
	* arm-tdep.h (arm_insert_single_step_breakpoint): Remove
	declaration.