core/blockly.js was removed from the ts/migration branch in PR #6261,
but for some reason when ts/migration was merged into develop via
a two step process something went wrong:
* as expected, blockly.js got renamed to blockly.ts in PR #6297, but
* for some reason it got re-added under its original name in PR #6299.
Since the file should not exist, is not used, and has proven to
cause confusion (to me at least!), delete it again, hopefully for
good this time.
c063d12abb