Remove null index values on normalized dataframe

[rwedge]

Fixes #1874

This PR doesn't address #1680 as with the NA index value removed from the dataframe at normalization, there's no NA-indexed data to group on, even if we enabled the NA GROUP

[tamargrey]

We can probably close #1873 now @dvreed77

[codecov]

Codecov Report

Merging #1897 (e72379b) into main (a8604d5) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1897   +/-   ##
=======================================
  Coverage   98.76%   98.77%           
=======================================
  Files         147      148    +1     
  Lines       16307    16355   +48     
=======================================
+ Hits        16106    16154   +48     
  Misses        201      201           

Impacted Files	Coverage Δ
featuretools/entityset/entityset.py	99.21% <100.00%> (+<0.01%)	⬆️
featuretools/primitives/__init__.py	100.00% <100.00%> (ø)
...ools/tests/entityset_tests/test_last_time_index.py	100.00% <100.00%> (ø)
...eaturetools/tests/entry_point_tests/test_plugin.py	100.00% <100.00%> (ø)
...retools/tests/entry_point_tests/test_primitives.py	100.00% <100.00%> (ø)
featuretools/tests/entry_point_tests/utils.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b5f0251...e72379b. Read the comment docs.

[rwedge]

doing the drop here might cause a scenario where make_secondary_time_index logic reintroduces null index values but I'm not positive

[rwedge]

any ideas on why upgrading to WW 0.12.0 would impact this test?

featuretools/featuretools/tests/entityset_tests/test_es.py

Lines 2175 to 2180 in 79eea5f

	def test_pd_es_pickling(pd_es):
	pkl = pickle.dumps(pd_es)
	unpickled = pickle.loads(pkl)
	assert pd_es.__eq__(unpickled, deep=True)
	assert not hasattr(unpickled, WW_SCHEMA_KEY)

Edit: appears to be an issue comparing the null tuples of LatLongs, introduced by alteryx/woodwork#1255

[tamargrey]

lgtm assuming tests pass!