core: Remove unused string

This was mistakenly added on https://github.com/CyanogenMod/android_frameworks_base/commit/9337d51a9ea31ab77392a3988446aadb57d4eba0

Change-Id: I6b2b2c0dabafa3537b8c5152e0393ef5c828e64b
Merge "core: Remove unused string" into cm-11.0