po: delete the ancient PO files for Indonesian and Nynorsk

These files haven't been updated in more than fifteen years and their
number of translated strings has dropped to below twenty percent.

Also, prevent them from coming back when next syncing with the TP.

po/LINGUAS

@@ -1,2 +1,2 @@
 # List of available languages.
-bg ca cs da de eo es eu fi fr ga gl hr hu id is it ja ko ms nb nl nn pl pt pt_BR ro ru sk sl sr sv tr uk vi zh_CN zh_TW
+bg ca cs da de eo es eu fi fr ga gl hr hu is it ja ko ms nb nl pl pt pt_BR ro ru sk sl sr sv tr uk vi zh_CN zh_TW

po/update_linguas.sh

@@ -9,6 +9,9 @@ rm *.po
 wget --recursive --level=1 --accept=po --no-directories --no-verbose \
        https://translationproject.org/latest/nano/  ||  exit 2
 
+# These PO files are less than twenty percent translated:
+rm -v  id.po  nn.po
+
 # Are there now PO files that are not in git yet?
 NEWSTUFF=$(git status --porcelain *.po | grep "^??")