Do not install init.rc for (vendor_)ramdisk variants.

Previously, the vendor_ramdisk variant of a module installs the
init.rc file to /vendor/etc/init.

In first stage init, no init rc files are read, so no init rc files
should be installed to any ramdisks.

This change removes LOCAL_INIT_RC for the (vendor_)ramdisk variant
of a module, so that init rc file is not installed for (vendor_)ramdisk
variant of a module.

Test: m snapuserd snapuserd.vendor_ramdisk
      and manually inspect the out directory
Fixes: 174587489
Change-Id: I71227d807244b6538be0d6acce5e94f129a86065