Remove legacy mediawiki core jobs

Stop triggering mediawiki-core-phpunit* and
mediawiki-core-install-sqlite jobs. They are superseeded by the Zuul
cloner based job mediawiki-vendor-integration which runs the whole test
suite.

The job pass on wmf branches.

Change-Id: Idf44bb9e6256818660cb04f090cf72dcbde0f421