librust_baremetal: No HAVE_ASSEMBLER___MEMCPY_CHK

Stop defining the unnecessary CPP macro.

Test: TH
Change-Id: Ided365bdd77854f3840ed865537ef43d7cdd00c3
diff --git a/libc/Android.bp b/libc/Android.bp
index f50d440..0bd1852 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -2284,7 +2284,6 @@
     ],
     arch: {
         arm64: {
-            cflags: ["-DHAVE_ASSEMBLER___MEMCPY_CHK"],
             srcs: [
                 "arch-arm64/string/__memcpy_chk.S",
             ],