i18n: better stripping of header comment for new translations

Also strip any header occurrence of:

  # FIRST AUTHOR <EMAIL@ADDRESS>, 2019.
  #

while preserving stripping of:

  #, fuzzy

and leading empty comment lines.

scripts/i18n_utils.py

@@ -36,7 +36,10 b" header_comment_strip_re = re.compile(r''"
     |
     ^
     [#][ ]FIRST[ ]AUTHOR[ ]<EMAIL@ADDRESS>,[ ]\d+[.] \n
-    [#] \n
+    (?:[#] \n)?
+    |
+    ^
+    (?:[#] \n)?
     [#],[ ]fuzzy \n
     ''',
     re.MULTILINE|re.VERBOSE)