update Mypy plugin status
update Mypy plugin status

The Mypy plugin is not maintainable long-term and will be replaced
by new APIs that allow for typing to work inline without the need
for plugins.

Change-Id: Icc7a203df1d0b19bde2fd852719b7b7215774c58
References: #7535

sqlalchemy/sqlalchemy,zzzeek/sqlalchemy