[mysql] Revert deprecation warning when using PyMySQL < 0.7.11
[mysql] Revert deprecation warning when using PyMySQL < 0.7.11

This partially reverts Change-Id: I550b7c56fcce1a5a50f8ea6d5a0c47b781f80dc3

The revert is made because current Toolforge installation supports
PyMySQL 0.7.10 currently and no warning should be printed in that case.

Bug: T216741
Change-Id: I0d436c4b5eca670c5ddfc86f3421528a72048160

wikimedia/pywikibot-core,wikimedia/pywikibot-core