Duplicate iscoroutinefunction/is_coroutine_function function

[jakirkham]

Appears we define this same function with slightly different names twice. If we need the two names, maybe one can be an alias. Otherwise maybe we drop one

distributed/distributed/utils.py

Lines 1346 to 1347 in 3407aa3

	def is_coroutine_function(f):
	return asyncio.iscoroutinefunction(f) or gen.is_coroutine_function(f)

distributed/distributed/utils.py

Lines 1249 to 1250 in 3407aa3

	def iscoroutinefunction(f):
	return inspect.iscoroutinefunction(f) or gen.is_coroutine_function(f)

cc @ian-r-rose @mrocklin