Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

…ions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

Also, make sure templates don't have copyrights.

…ll files

Remove copyrights from templates as otherwise it will cause these files not to match the files created during `flutter create` which will then cause our automigration code to fail.