vcrash should, like lcrash, delete the COW filesystem by default

[AdamBromiley]

Is your feature request related to a problem? Please describe.
The vhalt/lhalt programs do not delete the COW filesystem by default because they are used to avoid corrupting it for reuse across launches. Similarly, lcrash does delete the fs by default because it could leave it in an unstable state (though there's --keep-fs to prevent this).

For some reason, vcrash was chosen not to delete the fs by default. This is inconsistent.

Describe the solution you'd like
vhalt/lhalt keep the fs by default but have the --remove-fs option.
vcrash/lcrash remove the fs by default but have the --keep-fs option.