hurd: Fix spurious installation of headers defining hidden prototypes

	* sysdeps/mach/include/lock-intern.h: Move to include/.
	* sysdeps/mach/include/mach.h: Move to include/.
	* sysdeps/mach/include/mach/mig_support.h: Move to include/mach/.
	* sysdeps/mach/include/mach_error.h: Move to include/.