Obsolete information about differences with available SQL drivers

http://doc.qt.io/qt-5/sql-driver.html

Section "Supported Databases":

Due to license incompatibilities with the GPL, not all of the plugins are provided with Open Source Versions of Qt

But there is no difference between Open Source and Commercial version in terms of supplied SQL drivers. Maybe, in the past, but not now.

So, it's better to delete this sentence in order to prevent related questions from spawning.