[kcmkwin/compositing] Remove combobox to select between GLX and EGL
Summary:
The selection of whether GLX or EGL should be used doesn't work in
practice due to the following reasons:
- Intel/EGL/X11 results in rendering errors
- NVIDIA still doesn't support EGL
- OpenGLES forces to EGL (combobox only one entry)
- Wayland forces to EGL (combobox only one entry)
Offering the selection only offers the user a way to destroy the
system. We get too many bug reports about rendering errors and we
get too many complaints about this not working properly on social
media. E.g.: "The Meh: EGL mode causes bugs in the launcher"
The configuration interface showed a warning when selecting it, but
apparently users ignore warnings like "might be broken". If that's the
case let's better remove the option.
If users really want this they can still enable it manually through
editing the config file or through the env variable.
Change intended for Plasma/5.7 branch - I'm sick of users complaining
about it!
Test Plan: Opened KCM, verified Combobox is gone
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D2224