Remove duplicate strings.

"Yes" and "no" were redefined many times with no clear benefit, so this
consolidates them into one definition.

Bug: 243843096
Test: Build, install, and open the Settings app
Test: atest SettingsRoboTests
Change-Id: I5f84d09f223efd478461ded93aeac82bf7b128d8

tests/robotests/src/com/android/settings/wifi/WifiSummaryUpdaterTest.java

@@ -110,7 +110,7 @@ public class WifiSummaryUpdaterTest {
         mWifiTracker.enabled = false;
 
         assertThat(mSummaryUpdater.getSummary())
-            .isEqualTo(mContext.getString(R.string.switch_off_text));
+            .isEqualTo(mContext.getString(R.string.off));
     }
 
     @Test