ld: Remove emultempl/armcoff.em

Remove emultempl/armcoff.em which has been unused after

commit 2ac93be7
Author: Alan Modra <amodra@gmail.com>
Date:   Mon Apr 16 20:33:36 2018 +0930

    Remove arm-aout and arm-coff support

    This also removes arm-netbsd (not arm-netbsdelf!), arm-openbsd, and
    arm-riscix.  Those targets weren't on the obsolete list but they are
    all aout, and it doesn't make all that much sense to remove arm-aout
    without removing them too.

	* emultempl/armcoff.em: Removed.