Revert "Merge "add aiomysql support""

Revert "Merge "add aiomysql support""

This reverts commit 23343f87f3297ad31d7315ac0e5312db10ef7592, reversing
changes made to c5831b1abd98c46ef7eab7ee82ead18756aea112.

The crashes that occur in jenkins have not been solved and are
now impacting master.   I am not able to reproduce the failure,
including running on the CI machines directly, and a few runs
where I sat there for 20 minutes and watched, it didn't happen.
it is the ultimate heisenbug.

Additionally, there's a reference to "arraysize" that doesn't
exist in fetchmany() and there seem to be no tests that exercise
this for any DBAPI which is also a major bug to be fixed.

References: #5747