remove _pkgname_without_arch (and refs)

This function is old code that is unneeded due to changes in how salt
manages packages. It also represents a bug in which trying to use a
pkg.removed state using the pkgname:i386 format used by apt for 32-bit
packages on 64-bit systems always fails, because the package is
identified as pkgname, not pkgname:i386.  Additionally, using just
"pkgname" in your pkg.removed state would fail, because running "apt-get
remove pkgname" would fail for pkgname:i386.