[qpa] Don't specify EGL_SURFACE_TYPE when choosing EGLConfig

Summary:
Since QPA only performs off-screen rendering, it does not require an EGLConfig
that supports any particular surface type.  Currently it requests a config
supporting window surfaces, however the EGLDeviceEXT platform, which is the
basis of the EGLStream back-end used with the proprietary NVIDIA driver, does
not support such surfaces resulting in eglChooseConfig not returning any valid
configs when that back-end is in use. Since QPA doesn't actually create any
window surfaces, it should be fine to remove this restriction to allow it to
initialize properly with the EGLStream back-end.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin, davidedmundson

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D20455