Changed seconds calculation for timedelta.total_seconds()

Conflicts:
	sunpy/physics/transforms/differential_rotation.py
Removed the fixtures for 2.6 as they are not tested anymore
Removed an old work around to get test raised errors for 2.6
All old formating syntax (eg: "%s" % (var) ) has been changed to the
newer method: (eg: "{0}".format(var) ).  Also, some changes have been
done in some time formatings.
Merge pull request #1073 from dpshelio/TimeCalc_diffrot

[Review]: Removed all 2.6 heritage