ui: raise min SDK to 24

The difference between the usage of 21 and 24 is not big enough to hold
on to all the baggage from API 21

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

ui/src/main/java/com/wireguard/android/activity/TunnelToggleActivity.kt

@@ -22,7 +22,6 @@ import com.wireguard.android.backend.Tunnel
 import com.wireguard.android.util.ErrorMessages
 import kotlinx.coroutines.launch
 
-@RequiresApi(Build.VERSION_CODES.N)
 class TunnelToggleActivity : AppCompatActivity() {
     private val permissionActivityResultLauncher =
         registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { toggleTunnelWithPermissionsResult() }