exec.library: Allocate/Deallocate functions must remain generic and not handler MemHe...

exec.library: Allocate/Deallocate functions must remain generic and not handler MemHeaderAllocatorCtx

Both of those functions can be used by external code to work with
externally created MemHeaders. Because of that, those functions cannot
provide MemHeaderAllocatorCtx extension which is Exec internal concept.
Care needs to be taken inside Exec not to use those functions after
MemHeaderAllocatorCtx was associated with a given MemHeader.

git-svn-id: https://svn.aros.org/svn/aros/trunk/AROS@47116 fb15a70f-31f2-0310-bbcc-cdcc74a49acc