remove NPN bindings -- you should be using ALPN! (#4765)

* remove NPN bindings -- you should be using ALPN!

pyOpenSSL consumed these, but we've marked it as deprecated and it
already handles the case where the bindings are not available.

* set Cryptography_HAS_NEXTPROTONEG to 0 for pyOpenSSL

we can remove this symbol in like...5 years.

* remove another NPN related definition

* suspicious

* Revert "remove another NPN related definition"

This reverts commit d872a7d1d776858c77b8c607f63cc9b5fef1ae39.

Revert "suspicious"

This reverts commit 5b767484f1cde132f686600a46e61a18e33cbdae.