Remove redundant comment about version

The version is no longer duplicated in setup.cfg (since 5155ba7), so remove
redundant TODO suggesting folks update in two places.

Co-authored-by: Ofek Lev <ofekmeister@gmail.com>
Signed-off-by: Joshua Lock <jlock@vmware.com>

Author: joshuagl

tuf/__init__.py

@@ -5,7 +5,4 @@
 """
 
 # This value is used in the requests user agent.
-# setup.cfg has it hard-coded separately.
-# Currently, when the version is changed, it must be set in both locations.
-# TODO: Single-source the version number.
 __version__ = "1.0.0"