Refine the check restriction function in WifiEntryPreference

- Move checkRestrictionAndSetDisabled function from WifiEntryPreference to necessary child-classes to avoid impacting other child-classes such as SavedAccessPointsPreference.

- Avoid adding ShadowRestrictedPreference to the unnecessary test class.

Bug: 233871529
Test: manual test
make RunSettingsRoboTests

Change-Id: Ia2145401558b293b5f4eaa0860f83b7d3bbab548