arm: Remove ununsed ARM code in optimized implementation

This patch removes the ununsed ARM code path for armv6t2 memchr and
strlen and armv7 memch and strcmp.  In all implementation, the ARM
code is not used in any possible build (unless glibc is explicit
build with the non-documented NO_THUMB compiler flag) and for armv7
the resulting code either produces wrong results (memchr) and throw
build error (strcmp).

Checked on arm-linux-gnueabihf built targeting both armv6 and
armv7.

	* sysdeps/arm/armv6t2/memchr.S (memchr): Remove ARM code path.
	* sysdeps/arm/armv6t2/strlen.S (memchr): Likewise.
	* sysdeps/arm/armv7/multiarch/memchr_neon.S (memchr): Likewise.
	* sysdeps/arm/armv7/strcmp.S (strcmp): Likewise.