Support File deletion through VFS

[jetrotal]

Good for Savefiles deletion and other future features.
Cloning a savefile between slots could also be interesting.

[florianessl]

Something to note here, for future compatibility:
The "PPCOMP" tool (PR #3363) already features commands for deleting & copying save files. Though I skipped on the implementation of those two because I couldn't find any examples for games that use them.

EDIT:
Looks like the use case for deleting save files has also be mentioned here before: #2671