Revert D136292 "[libc] mem* framework v3"

This breaks llvm-libc build bots:
 - libc-x86_64-debian-dbg-asan
 - libc-x86_64-debian-fullbuild-dbg-asan
Address sanitizers fail with "AddressSanitizer: invalid alignment requested in aligned_alloc: 64, alignment must be a power of two and the requested size 0x41 must be a multiple of alignment (thread T0)"
 - libc-aarch64-ubuntu-dbg
 - libc-aarch64-ubuntu-fullbuild-dbg
https://lab.llvm.org/buildbot/#/builders/223/builds/8877/steps/7/logs/stdio
 - libc-arm32-debian-dbg
https://lab.llvm.org/buildbot/#/builders/229/builds/5201/steps/7/logs/stdio

This reverts commit 903cc71.

Author: gchatelet

libc/src/string/memory_utils/CMakeLists.txt

@@ -2,17 +2,13 @@
 add_header_library(
   memory_utils
   HDRS
+    utils.h
+    elements.h
     bcmp_implementations.h
     bzero_implementations.h
-    elements.h
     memcmp_implementations.h
     memcpy_implementations.h
     memset_implementations.h
-    op_aarch64.h
-    op_builtin.h
-    op_generic.h
-    op_x86.h
-    utils.h
   DEPS
     libc.src.__support.CPP.bit
 )