bookmarks: remove redundant check for newline

New bookmarks are already checked for illegal characters (':', '\0',
'\n', and '\r') in bookmarks.valid().

mercurial/commands.py

@@ -790,8 +790,6 b' def bookmark(ui, repo, mark=None, rev=No'
     cur   = repo.changectx('.').node()
 
     def checkformat(mark):
-        if "\n" in mark:
-            raise util.Abort(_("bookmark name cannot contain newlines"))
         mark = mark.strip()
         if not mark:
             raise util.Abort(_("bookmark names cannot consist entirely of "

tests/test-bookmarks.t

@@ -214,12 +214,12 b' reject bookmark name with newline'
 
   $ hg bookmark '
   > '
-  abort: bookmark name cannot contain newlines
+  abort: bookmark names cannot consist entirely of whitespace
   [255]
 
   $ hg bookmark -m Z '
   > '
-  abort: bookmark name cannot contain newlines
+  abort: bookmark names cannot consist entirely of whitespace
   [255]
 
 bookmark with existing name