Remove MySQL-related tests, code, and documentation

[Andersson007]

Remove MySQL-related tests, code, and documentation. Needs to be done in a few steps:

1. Remove mysql-related blocks, tasks, and functions from test matrix, integration, and unit tests
2. Remove mysql-related code from modules
   2.1. Remove mysql-specific arguments and all mentions of MySQL from modules' DOCUMENTATION and EXAMPLES blocks
3. Remove mysql-related code from module_utils