Remove duplicated code in InputMethodSubtypeSwitchingController

InputMethodSubtypeSwitchingController#parseLanguageFromLocaleString is
already defined in LocaleUtils.

Bug: 303302694
Test: atest FrameworksServicesTests:com.android.server.inputmethod.LocaleUtilsTest
Change-Id: I67ec553f8cfc21b1916a5a32783630ea43f2d407
3 files changed