Do not populate `ro.kernel.qemu` in `ProcessKernelCmdline`

The emulator migrated to `ro.boot.qemu`.

Bug: 182291166
Test: presubmit
Signed-off-by: Roman Kiryanov <rkir@google.com>
Change-Id: Iaa3bdff5cc1efa79c21ae2dc2bdf7ec74731f66c