GL: Remove ARB_base_instance check for EXT_base_instance support This is a speculative fix for reported flickering issues on Linux. https://chromium-review.googlesource.com/c/angle/angle/+/6580170 changed EXT_base_instance to only be supported when it is not emulated and fixed the condition to include ARB_base_instance, possibly hitting driver bugs on some devices. Bug: angleproject:355645824 Bug: chromium:427956856 Change-Id: I869fa7f618e82ad46c1953f0bacef0767bbc793e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6777576 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>