* ENH: update grammar for py39
Grammar is copied from cpython commit
b4e68960b90627422325fdb75f463df1e4153c6e
There appears to be 3 new tokens in the grammar (ASYNC, AWAIT, and
TYPE_COMMENT)
* MNT: revert back to py38 grammar as py39 grammar pt1: comments
Looks like upstream has added some comments, remove them
* MNT: remove TYPE_COMMENT added upstream
* MNT: add string / fstring related changes from parso 38 grammer
* MNT: remove changes to support upstream grammar file