Remove unused references to system.powerSource.
Remove unused references to system.powerSource.

PiperOrigin-RevId: 357022100

nawawi/closure-compiler,ChadKillingsworth/closure-compiler,monetate/closure-compiler,monetate/closure-compiler,monetate/closure-compiler,google/closure-compiler,nawawi/closure-compiler,nawawi/closure-compiler,google/closure-compiler,ChadKillingsworth/closure-compiler,google/closure-compiler,ChadKillingsworth/closure-compiler,google/closure-compiler,ChadKillingsworth/closure-compiler,monetate/closure-compiler,nawawi/closure-compiler