Remove an unnecessary file

macho/arch/README.md

@@ -1,7 +0,0 @@
-# Targets
-
-This directory contains one file per instruction set. Each file defines a
-type for the target it supports, and the types implement `Target` from
-[`mod.rs`](mod.rs), which holds the constants and code that differ between
-targets. The rest of the linker is generic over it. The crates under
-[`arch/`](../../arch/) instantiate the linker for each type.