wiki/src/install/**/*.po: remove obsolete (#~) strings.
During the "scan" phase, ikiwiki first scans raw PO files, including these obsolete strings. We have "[[!command]]" ikiwiki directives split over multiple strings, so in these raw PO files, a directive can be started ("[[!command") but never closed ("]]"), which can cause this warning: Complex regular subexpression recursion limit (32766) exceeded at /usr/share/perl5/IkiWiki.pm line 1754. I suspect that other kinds of power-usage of ikiwiki + PO files can trigger this problem; let's fix this one to start with and see what happens then. refs: #16847