Update github.com/go-sql-driver/mysql to latest tagged release

[cpu]

Self-explanatory. We current use an explicit commit and should transition to v1.4.1

[jsha]

Unfortunately v1.4.1 pulls in an unneeded dependency on google.golang.org/appengine. That dependency is removed in master. I've asked the maintainers to tag a new release.

[jsha]

Some interesting PRs we'll pick up with the upgrade:

Remove strict mode - go-sql-driver/mysql#676
context.Context support - go-sql-driver/mysql#608, go-sql-driver/mysql#612, go-sql-driver/mysql#627, go-sql-driver/mysql#761)

[cpu]

I've asked the maintainers to tag a new release.

It looks like that request was closed as a dupe of one open since April 2019 :-/ If we're likely to be blocked for months+ on a new tag maybe we should consider alternatives (pinning a revision, eating the unneeded dep?)