patch 8.0.0726: translations cleanup script is too conservative

Problem:    Translations cleanup script is too conservative.
Solution:   Also delete untranslated messages.

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

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    726,
 /**/
     725,
 /**/