Housekeeping: Remove unused DB clients

[Net-burst]

🔧 Type of changes

• new bid adapter
• bid adapter update
• new feature
• new analytics adapter
• new module
• module update
• bugfix
• documentation
• configuration
• dependency update
• tech debt (test coverage, refactorings, etc.)

✨ What's the context?

PBS uses asynchronous VertX DB clients. For some reason we had synchronous MySQL and PostgreSQL clients defined in pom.xml

🧠 Rationale behind the change

Those 2 dependencies are unused. If private fork would want to use synchronous DB clients for some reason, they can re-add the dependencies.

🔎 New Bid Adapter Checklist

• verify email contact works
• NO fully dynamic hostnames
• geographic host parameters are NOT required
• direct use of HTTP is prohibited - implement an existing Bidder interface that will do all the job
• if the ORTB is just forwarded to the endpoint, use the generic adapter - define the new adapter as the alias of the generic adapter
• cover an adapter configuration with an integration test

🧪 Test plan

Existing tests should be more than enough.

🏎 Quality check

• Are your changes following our code style guidelines?
• Are there any breaking changes in your code?
• Does your test coverage exceed 90%?
• Are there any erroneous console logs, debuggers or leftover code in your changes?

[osulzhenko]

@Net-burst we need those dependencies for functional tests — maybe just use test scope?
#4017

[Net-burst]

Closing as this is superseeded by #4017