qubes/vm: remove special case for 'meminfo-writer' feature
qubes/vm: remove special case for 'meminfo-writer' feature

It should be either in a plugin, or handled entirely from inside of VM.
But surely not in main QubesVM class.

Fixes QubesOS/qubes-issues#2101

QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,marmarek/qubes-core-admin