Remove ODR violation with arm64 memrchr.

I haven't seen this cause a problem in practice --- I noticed this while
looking at something else entirely.

Test: llvm-objdump
Change-Id: I56e38165f45554ede538a50439f8e8ffe72871c8

libc/Android.bp

diff --git a/libc/Android.bp b/libc/Android.bp
index 139fd0e..02e3e11 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -661,7 +661,6 @@
         },
         arm64: {
             srcs: [
-                "upstream-openbsd/lib/libc/string/memrchr.c",
                 "upstream-openbsd/lib/libc/string/strcat.c",
                 "upstream-openbsd/lib/libc/string/stpncpy.c",
                 "upstream-openbsd/lib/libc/string/strlcat.c",