tclpkg vgpanecmd: remove acceptance of ambiguous abbreviated commands
`vgpanecmd` accepted abbreviations of commands, e.g. `li` for list. However
these abbreviations were accepted as first match with no disambiguation. So `r`
would always be interpreted as `rotate`, not `remove`. This behavior appears to
be an unintentional side effect of commands being incrementally introduced over
time without this kind of prefix-matching overlap being taken into account,
though this is mostly a guess as all this code was implemented prior to the
first Git commit.