Remove unused lua-facing `crawl.formatted_mpr`

As far as I can tell, the last and only use of this was removed in
3ee907b3d4405c3d89ec2948dc2b99d798e98b9d.
=== Branch-specific commits ===
create_pot
exclude.pot
messages.pot
Define customary `_` shortcut for gettext calls

Right now i'm planning to only use _() on string-like literals and
calling regular gettext() for variables.
`no_()` gettext noop

To be used for extracting strings that are not directly passed to
gettext when defined, or used in both translated and untranslated form.
Remove empty mpr("")

To make create_pot do something.
Unconditionally translate mpr() and friends
Somewhat more complicated mprf->mpr conversion (falling down stairs)
Split some arena and sanctuary string building

Not like arena is a prime target for translations, but...
Split some ternary `mpr` into if/else constructs

Translation preparations, mostly. Complete strings are far easier to
understand and therefore translate, and sentence-building code is hard
enough to write for the cases where we actually need it.

Plain code rearrangements happened to ease automated string extraction.
Even more splitting and refactoring for strings (TODO Review!)
Split armour un-/equip prompt handling into separate `yesno`
Split butcher delay handling into several `mpr` (plural!)
Split mushroom spawn messages into several `mpr` (plural!)
Some more splitting
Split crawling mess (TODO Review)
Split crawling mess (Another one, TODO Review)

This is the first actual loss in that _count_article is no longer.
Honestly not bad news given just how overengineered the entire messaging
construct felt, and certainly impossible to make translatable here.

Seemingly random decisions between definite and indefinite article was
made after very short in-game testing, happy about changes there.
Ideally we would not duplicate the whole structure just because it is
decided that supporting both would be nice, however.
Discharge