style: drop requirement to only use single lines between top-level objects

Differential Revision: https://phab.mercurial-scm.org/D5105

contrib/check-commit

@@ -39,8 +39,6 b' errors = ['
      "summary keyword should be most user-relevant one-word command or topic"),
     (afterheader + r".*\.\s*\n", "don't add trailing period on summary line"),
     (afterheader + r".{79,}", "summary line too long (limit is 78)"),
-    (r"\n\+\n( |\+)\n", "adds double empty line"),
-    (r"\n \n\+\n", "adds double empty line"),
     # Forbid "_" in function name.
     #
     # We skip the check for cffi related functions. They use names mapping the