mail/mutt: Update to 2.0.0 with extra patch cleanup

• Update to 2.0.0 [1][2]
• Remove threadcomplete. Appears ~(~T) has the same functionality.
• Remove muttlib.c patch and use mutt's mktemp functions for temp files. I don't believe this is an issue since neomutt also use's mutt's.
• Remove forcebase64 patch. Should no longer be an issue.
• Remove spelling options. Install the desired spelling port and configure mutt as needed.
• Update patch contexts.

[1] https://marc.info/?l=mutt-announce&m=160478560100820&w=2
[2] http://www.mutt.org/relnotes/2.0/

PR: 250970
Submitted by: Derek Schrock <dereks@lifeofadishwasher.com> (maintainer)