Revert "Add URL to Wikia Extensions and $wgExtensionCredits to some that...

Reverts Wikia/app#5745 because it breaks `dev` branch with PHP syntax for example:
* `Parse error: syntax error, unexpected '"url"' (T_CONSTANT_ENCAPSED_STRING), expecting ')' in /usr/wikia/source/app/extensions/wikia/MultiTasks/SpecialMultiWikiFinder.php on line 25`,
* `Parse error: syntax error, unexpected '' (T_ENCAPSED_AND_WHITESPACE), expecting identifier (T_STRING) or variable (T_VARIABLE) or number (T_NUM_STRING) in /usr/wikia/source/app/extensions/wikia/AutoMainpageFixer/AutoMainpageFixer.php on line 20`.

A good practice is to smoke test branch after changing so many files or even run a unit tests against it.