remove "export to file" code path from export operation

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/util/ExportHelper.java

@@ -96,7 +96,7 @@ public class ExportHelper
 
     @Override
     public ExportKeyringParcel createOperationInput() {
-        return new ExportKeyringParcel(mMasterKeyIds, mExportSecret, mExportFile.getAbsolutePath());
+        return new ExportKeyringParcel(mMasterKeyIds, mExportSecret, Uri.fromFile(mExportFile));
     }
 
     @Override