Remove usages of LPU.savedPatternExists

The correct method to call is isLockPatternEnabled, which
also checks whether we've actually selected a pattern.

Also removes the code for the obsolete pattern enabled setting.

Bug: 18931518
Change-Id: I6f369eb60f8f6bb1e33384cd06534c713ab52e79

src/com/android/settings/ChooseLockPattern.java

@@ -567,7 +567,6 @@ public class ChooseLockPattern extends SettingsActivity {
             final boolean required = getActivity().getIntent().getBooleanExtra(
                     EncryptionInterstitial.EXTRA_REQUIRE_PASSWORD, true);
             utils.setCredentialRequiredToDecrypt(required);
-            utils.setLockPatternEnabled(true);
             utils.saveLockPattern(mChosenPattern);
 
             if (lockVirgin) {