Remove validate-jquery-uncompressed.js

Based on some discussions in PR #2293.

The file `media/system/js/validate-jquery-uncompressed.js` was added unintended together with PR #1842.
It's not used anywhere in core and there is no API to use that file.

The correct file to use is `validate-uncompressed.js` (and `validate.js`) which is converted to jQuery in Joomla! 3.3.0.

This PR removes the unneeded file.
Validation should work as it did before applying the patch.