patch 8.0.0726: translations cleanup script is too conservative

Problem:    Translations cleanup script is too conservative.
Solution:   Also delete untranslated messages.
diff --git a/src/po/cleanup.vim b/src/po/cleanup.vim
index 24ae74e..b27d880 100644
--- a/src/po/cleanup.vim
+++ b/src/po/cleanup.vim
@@ -8,12 +8,18 @@
 let s:was_diff = &diff
 setl nodiff
 
-silent g/^#: /d
+" untranslated message preceded by c-format or comment
+silent g/^#, c-format\n#/.d
+silent g/^#\..*\n#/.d
+
+silent g/^#[:~] /d
 silent g/^#, fuzzy\(, .*\)\=\nmsgid ""\@!/.+1,/^$/-1s/^/#\~ /
 silent g/^msgstr"/s//msgstr "/
 silent g/^msgid"/s//msgid "/
 silent g/^msgstr ""\(\n"\)\@!/?^msgid?,.s/^/#\~ /
 
+silent g/^\n\n\n/.d
+
 if s:was_diff
   setl diff
 endif