Free pointers in parser activations (#4486)

[adrianeboyd]

Description

Backport 3dfc764 to v2.1.x:

• Free pointers in ActivationsC

• Restructure alloc/free for parser activations

• Rewrite/restructure to have allocation and free in parallel functions
  in _parser_model rather than partially in _parseC() in Parser.

• Remove resize_activations from _parser_model.pxd.

Fixes #4538.

Types of change

Checklist

• I have submitted the spaCy Contributor Agreement.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[ines]

Ugh, the test failure here is some pytest version compatibility stuff... I remember this coming up before. Let me see how I fixed this. I think all we need to do is upgrade the pytest requirement.

[adrianeboyd]

Yeah, I ran the tests but probably didn't downgrade pytest.

[honnibal]

I wouldn't worry about the failure on 3.5 OSX. It's because our wheels don't work there, and it's failing to compile Thinc on that platform. It's fine to release with that test failing.

[kabirkhan]

Haha, our time difference is pretty evident here. Thank you all for the quick responses and for getting this out. Really appreciate the fast turnaround!