emacs: Fontify From with message-header-other

emacs: Fontify From with message-header-other

Commit e26d767897e8ab59f05808a12ac5c9c1e3c7030f changed the
fontification of the body associated with the From header to
message-header-from.  However, that face is non-existent, and in
message.el (message-font-lock-keywords) the From-header falls through
and is attributed the message-header-other face.

This commit removes the fontification of the [Ff]rom header in
notmuch-show-mode in order to fontify it using the message-header-other
face.

This only affects non-default configurations where
notmuch-message-headers is set to display From.