Fix generation and translation of desktop file

a91c4f70c3 switched processing of the
desktop file from intltool to gettext-backed i18n.merge_file and dropped
leading underscores which used to be processed by intltool.

However, this commit omitted dropping the underscore from Keywords,
resulting in this field being stripped from the installed version.

Furthermore, make_pot.sh was broken since it too relied on the
underscore meaning POT regeneration will now remove the desktop files
strings from translation files.
Since it was not added to po/POTFILES meson’s native aegisub-pot target
also doesn't add desktop file strings to the translation pool. Though,
this target still misses a lot of other strings as well and shouldn't be
used yet anyway.

This commit removes leftover underscores and reintegrates desktop file
strings into both make_pot.sh. Integration into aegisub-pot is done in a
follow-up commit.

packages/desktop/aegisub.desktop.template.in

@@ -9,7 +9,7 @@ TryExec=@AEGISUB_COMMAND@
 Icon=aegisub
 Terminal=false
 Categories=AudioVideo;AudioVideoEditing;GTK;
-_Keywords=subtitles;subtitle;captions;captioning;video;audio;
+Keywords=subtitles;subtitle;captions;captioning;video;audio;
 MimeType=application/x-srt;text/plain;text/x-ass;text/x-microdvd;text/x-ssa;
 StartupNotify=true
 StartupWMClass=aegisub

po/make_pot.sh

@@ -41,7 +41,7 @@ find ../automation -name *.lua \
 
 for i in 'Name' 'GenericName' 'Comment' 'Keywords'
 do
-  grep ^_$i -n ../packages/desktop/aegisub.desktop.template.in \
+  grep ^$i -n ../packages/desktop/aegisub.desktop.template.in \
     | sed 's/\([0-9]\+\):[^=]\+=\(.*\)$/aegisub.desktop|\1|"\2"/' \
     | maybe_append
 done