Removed the UCI code to read the signatur (= name) from ~/.signature.

Removed the UCI code to read the signatur (= name) from ~/.signature.
If we want to read something from ~/.signature, then those lines that
form the footer of a mail message. What is called ``signature'' here
is the name of the sender; the name that is put into the From: line.
There are already several options to put it:
- environment variable: SIGNATURE (to change temporary)
- profile entry: Signature: (to set only for the mail system)
- GECOS field in passwd (fallback and global)
These should be enough.