Revert "kernel-install: Add KERNEL_INSTALL_NOOP (#4103)"

Further discussion showed that this better gets addressed at the packaging
level.

This reverts commit 34210af7c6.

src/kernel-install/kernel-install

@@ -61,13 +61,6 @@ for i in "$@"; do
     fi
 done
 
-# KERNEL_INSTALL_NOOP may be used by programs like lorax and rpm-ostree which
-# want to install a kernel (indirectly via RPM), but control generation of the
-# initramfs.  In general, OSTree takes over kernel management too.
-if test -n "${KERNEL_INSTALL_NOOP:-}"; then
-    exit 0
-fi
-
 if [[ "${0##*/}" == 'installkernel' ]]; then
     COMMAND='add'
 else