libc: remove most dynamically-selected x86 atom functions

The 'generic' versions of these all have newer impls from Intel, and
seemingly use the same feature baseline (sse2 or ssse3). There's
no obvious reason to carry these old impls around.

While I'm here, also remove the ssse3-memcpy. While that might be
a bit faster, `s/memmove/memcpy` seems slightly risky for 32-bit x86.

Bug: 358360849
Test: mma
Change-Id: I62cbf638bf4d9fdb799af93168b0cc0ea841526f
diff --git a/libc/arch-x86/string/sse2-strcpy-slm.S b/libc/arch-x86/string/sse2-strcpy-slm.S
index 22ceeab..b5d84b5 100644
--- a/libc/arch-x86/string/sse2-strcpy-slm.S
+++ b/libc/arch-x86/string/sse2-strcpy-slm.S
@@ -79,7 +79,7 @@
 #define POP(REG) popl REG; CFI_POP (REG)
 
 #ifndef STRCPY
-# define STRCPY  strcpy_generic
+# define STRCPY  strcpy
 #endif
 
 #ifdef USE_AS_STPNCPY