Remove inapplicable path access checks in testExternalStorageNone

Before R, app without storage permission didn't have access to external
storage directory. In R, apps can contribute to media and will have
access permissions to its files in external storage directory. Checking
for no access to paths in external storage directory is not applicable in R.
Test: atest ExternalStorageHostTest#testExternalStorageNone
Bug: 147091021
Bug: 148918640

Change-Id: I8b8e16b96a5b7bf736769c1db2dc1941583201d6