Fix message-* user options that differ from Gnus trunk.

Fix message-* user options that differ from Gnus trunk.

message.el (message-from-style, message-interactive, message-signature): Remove comment.
message.el (message-cite-prefix-regexp): Default to mail-citation-prefix-regexp always.
message.el (message-sendmail-envelope-from): Comment fix.
message.el (message-yank-prefix): Default to mail-yank-prefix always.
message.el (message-indentation-spaces): Default to mail-indentation-spaces always.
message.el (message-signature-file): Default to mail-signature-file always.
sendmail.el (mail-citation-prefix-regexp): Remove "}" from citation prefix.