regroup mediawiki-core-jslint jobs definition

The mediawiki-core-jslint job definition was declared twice. Regroup the
parameters in a single entry.  Fix lint check:

voluptuous.voluptuous.Invalid: Duplicate name: mediawiki-core-jslint @
data['jobs'][20]

Change-Id: I589263e05880a6938d8839e17a22694b131d156e