Cleanup extra logic that handle python <=3.3

[Carreau]

#10833 dis most of that but there seem to be some logic still handling python 3.3

ipython/IPython/core/extensions.py

Lines 17 to 21 in dda5238

	try:
	from importlib import reload
	except ImportError :
	## deprecated since 3.4
	from imp import reload

ipython/IPython/utils/openpy.py

Lines 117 to 121 in dda5238

	try:
	from importlib.util import source_from_cache, cache_from_source
	except ImportError :
	## deprecated since 3.4
	from imp import source_from_cache, cache_from_source

ipython/IPython/utils/text.py

Lines 512 to 519 in dda5238

	#XXX: As of Python 3.4, the format string parsing no longer splits on a colon
	# inside [], so EvalFormatter can handle slicing. Once we only support 3.4 and
	# above, it should be possible to remove FullEvalFormatter.
	class FullEvalFormatter(Formatter):
	"""A String Formatter that allows evaluation of simple expressions.
	Any time a format key is not found in the kwargs,

(3.4.2+)

ipython/IPython/core/magics/execution.py

Lines 145 to 149 in dda5238

	# Timer.timeit copied from CPython 3.4.2
	def timeit(self, number=timeit.default_number):
	"""Time 'number' executions of the main statement.
	To be precise, this executes the setup statement once, and

There are possibly other places, this should be relatively easy to fix for a new contributor.

Each of these removal can be a separate PR.

[subhrm]

I would try to clean them up with separate PRs for each fix.

[subhrm]

I have now created two pull requests for fixes in IPython/core/extensions.py and IPython/utils/openpy.py. Based on the feedback from the maintainers, I would proceed to clean up rest of the files.