Remove arm_arch.h symlink.

The symlink is now dead. BoringSSL has already since been tweaked to include it
via <openssl/arm_arch.h> in the assembly files, so the existing -I lines pick it up.

Change-Id: If7d3cf81cc58eb2f61bb7d47add1552e4c21c59d
diff --git a/arm_arch.h b/arm_arch.h
deleted file mode 120000
index 3958887..0000000
--- a/arm_arch.h
+++ /dev/null
@@ -1 +0,0 @@
-src/crypto/arm_arch.h
\ No newline at end of file