WifiInstaller: add permission for access downloaded files

The previous fix for the security vulnerability b/33178389
add the code to drop the downloaded installation file but
forget to update the manifest for additional permission.  This
omission was due to that the original fix was merged from
mnc-dev, which doesn't have such permission requirement.

So add the required permission for deleting downloaded
installation file.

Bug: 33178389
Test: Verify WifiInstaller works and not crashing due permission
      denied exception

Change-Id: I987ad73dde0e3cc5b920cd08830dd065c47be402
(cherry picked from commit 9a9e51727a5cdaf3ac10c98e1ea4661bc13a11c7)
1 file changed