Remove in favor of similar, but more visible "--no-install" option for
"pmbootstrap flasher" and "pmbootstrap export".
It seems that the option wasn't really used by anybody, so let's just
remove it without a deprication period. If dear reader thinks otherwise
after this is merged, and is not happy with "--no-install", please state
your reasoning in a new issue, so we can discuss it.
Related: !1863
2f01c91c1a