Revert "PLATFORM-354 - somehow, ParsoidCacheUpdateTask is getting instantiated on wikis that have $wgEnableVisualEditorUI set to false. for now, moving task so it's available anywhere to prevent fatals. @inez - any idea how this can happen?"

This reverts commit 7ee6dc19166d46731747f853ea4f89b2458f976e.

(cherry picked from commit 3c0cb1d393579a2dd0039d804e1c7d2da25b73bc)
Revert "Revert "PLATFORM-354 - somehow, ParsoidCacheUpdateTask is getting instantiated on wikis that have $wgEnableVisualEditorUI set to false. for now, moving task so it's available anywhere to prevent fatals. @inez - any idea how this can happen?""

This reverts commit 3c0cb1d393579a2dd0039d804e1c7d2da25b73bc.

(cherry picked from commit a29d5e66d81b1d496b4edaf410b4109214f527ac)
adding stub class so jobs in the queue do not fail

(cherry picked from commit f8d9c9267baa9f08f7e3d93f19c01ba4cb1e1152)
Revert "adding stub class so jobs in the queue do not fail"

This reverts commit 133fa9f2a313ac9fc98baa9e1bfb3b590218b064.