reverts Concurrency works

reverts Concurrency works

trunk is frozen pending stabilisation so we can release MediaWiki 1.19.
Those changes introduces API changes and new SQL tables, so that sounds like
new feature we do not have time to review right now.

Please reapply changes in branches/concurrency and have code review handled
there. Once the branch has been reviewed, please hold. Once trunk is stable
enough and 1.19 got branched, you are welcome to merge the branch in trunk.

Note: we can have a Jenkins jobs setup to run the branch tests if you need.

Reverts:
r108595 r108591 r108585 r108584 108572 r108564 108560 r108559