Revert "Fixup commit for MFC vs HEAD conflict."

This reverts commit 67ba11269899896934089cca33a4e64ecac8f725.
Revert "Give mtx(9) the ability to crunch different type of structures, with the"

This reverts commit 4748e4076dbd8848394361613a506e1ddc603855.
Revert "Introduce macro stubs in the mutex implementation that will be always"

This reverts commit 503239f589ba824d5e7f469ef4fc5df606cee7a0.
Revert "Rework the known mutexes to benefit about staying on their own"

This reverts commit 7e40f737297c4cbf6f7de1f7a870551aa1bfb099.
Fix build with reverted mutex KPI.