Item9693: Remove requiremnt for Digest::SHA1

Digest::SHA is part of perl core and provides the SHA1 method.  I don't
find anywhere that Foswiki uses Digest::SHA1 explicitly.

git-svn-id: http://svn.foswiki.org/trunk/core@17209 0b4bb1d4-4e5a-0410-9cc4-b2b747904278