Remove x86 ifunc-defines.sym and rtld-global-offsets.sym

Merge x86 ifunc-defines.sym with x86 cpu-features-offsets.sym.  Remove
x86 ifunc-defines.sym and rtld-global-offsets.sym.  No code changes on
i686 and x86-64.

	* sysdeps/i386/i686/multiarch/Makefile (gen-as-const-headers):
	Remove ifunc-defines.sym.
	* sysdeps/x86_64/multiarch/Makefile (gen-as-const-headers):
	Likewise.
	* sysdeps/i386/i686/multiarch/ifunc-defines.sym: Removed.
	* sysdeps/x86/rtld-global-offsets.sym: Likewise.
	* sysdeps/x86_64/multiarch/ifunc-defines.sym: Likewise.
	* sysdeps/x86/Makefile (gen-as-const-headers): Remove
	rtld-global-offsets.sym.
	* sysdeps/x86_64/multiarch/ifunc-defines.sym: Merged with ...
	* sysdeps/x86/cpu-features-offsets.sym: This.
	* sysdeps/x86/cpu-features.h: Include <cpu-features-offsets.h>
	instead of <ifunc-defines.h> and <rtld-global-offsets.h>.