Refresh sh wrapper

For a while, the preferred installation method was via a Phar archive and the only feature we missed from `bin/wp` was support for the `WP_CLI_PHP` environment variable.

I think it's time to give it a scrub:

* [x] remove the COLUMNS handling (already handled by php-cli-tools)
* [ ] remove the over-complicated php.ini stuff

History for the original Drush code: https://github.com/msonnabaum/drush/blame/master/drush