Remove UNSAFE_ABI mode Our ABI has diverged enough that this is unlikely to work and is more scary than it was before.

Python 3.10.0a6 

Python 3.9.2 

Python 3.8.8 

Python 3.9.2rc1 

Python 3.8.8rc1 

Python 3.7.10 

Python 3.6.13 

Python 3.10.0a5 

the end of the 2.7 branch