Use Build.IS_EMULATOR to detect if a device is emulator

we already have it implemnted, remove copypasta.

Bug: 314168562
Test: boot emulator, check if emulator specific codepaths are activated
Change-Id: Iab31c97b09d247e04e7faa608b87463cb86806d1
Signed-off-by: Roman Kiryanov <rkir@google.com>