Update and review translations

[inkydragon]

• Check if pre-defined targets aegisub-pot, aegisub-update-po works.
  https://mesonbuild.com/i18n-module.html
• Remove or update po\make_pot.sh
• Add new target po\stats.sh
• Check if the GUI has been fully translated and then decide whether to delete those lines or not.

Aegisub/packages/win_installer/fragment_translations.iss

Line 38 in 7e9c7d7

#ifdef ENABLE_WX_TRANSLATIONS

xref: #119 (comment)

[CoffeeFlux]

There's also a default ninja target for generating the pot file and updating the PO files I believe. Not sure if that's workable or if we need the script; I haven't really looked at it much.