Allow user to turn off safe mode on Android 10 (Mar 2020 or newer)

Fixes #153.

Basically, this "forward"-ports a workaround for Android 9- thanks to Jimmy Chen.
As a consequence, #31 might reoccur if you turn off safe mode.

mobile/src/main/java/be/mygod/vpnhotspot/SettingsPreferenceFragment.kt

@@ -74,6 +74,10 @@ class SettingsPreferenceFragment : PreferenceFragmentCompat() {
             }
             boot.isChecked = BootReceiver.enabled
         } else boot.parent!!.removePreference(boot)
+        if (!RepeaterService.supported || !RepeaterService.safeModeConfigurable) {
+            val safeMode = findPreference<Preference>(RepeaterService.KEY_SAFE_MODE)!!
+            safeMode.parent!!.removePreference(safeMode)
+        }
         findPreference<Preference>("service.clean")!!.setOnPreferenceClickListener {
             GlobalScope.launch { RoutingManager.clean() }
             true