Fix reference to missing string

AAPT2 is about to be fixed to remove strings with no default
specified, which is always intended to be a string removal, where the
translations are left behind to be cleaned up at a later translation
update.

Fix this breakage introduced by ag/3646913

Bug: 36572857
Test: builds
Change-Id: I21030aa174daeff6841e9255d490bbd6c9a2aee7