Decision for 5.5 is to remove the Forum from the bundle (and the packs). Atm it has not been decided that we officially deprecate the Forum but it will not be released with 5.5.
In case a customer still wants to use the Forum with 5.5 he should still be able to add the admin-legacy and forum modules.
Somewhen in Q4/2016 the decision should happen if we want to invest into the Forum and refactor it completely or deprecate it officially.

Proposed solution

Remove all code which relies on admin-legacy. This will break functionality in the Forum Module but should have no effect on the commenting module.

(Originally DEV-277)