remove reference to logo from README
remove reference to logo from README

Since there is no longer a copy of the Python logo stored in this repository, remove the reference to it from the README
behrtam/xpython,exercism/xpython,jmluy/xpython,behrtam/xpython,exercism/xpython,exercism/python,N-Parsons/exercism-python,smalley/python,N-Parsons/exercism-python,exercism/python,jmluy/xpython,smalley/python