[Wi-Fi DPP] Refine code

Remove unused code.
Rename some variables and methods for better readability.
Fix typos.
Reduce unnecessary variable scope and method scope.
Simplify some code logic.

Bug: 120645817
Test: atest com.android.settings.wifi.dpp
Change-Id: I8f30b3e445f25ada927e995befee1783d2270b91

tests/unit/src/com/android/settings/wifi/dpp/WifiNetworkListFragmentTest.java

@@ -107,8 +107,6 @@ public class WifiNetworkListFragmentTest {
         intent.setData(Uri.parse(uriString));
         mActivityRule.launchActivity(intent);
 
-        verify(mWifiTracker).getManager();
-
         List<Fragment> fragments =
                 mActivityRule.getActivity().getSupportFragmentManager().getFragments();
         assertThat(fragments.size()).isEqualTo(1);