Vulkan: Reduce getMaxConformantESVersion() to 2.0 We are currently returning a 3.0 context for Vulkan backends (issue 3425). However, we aren't quite 3.0 conformant yet, so this bug will drop that back down to 2.0 in getMaxConformantESVersion(). Bug: angleproject:3734 Test: dEQP Change-Id: I2c5a6ee0ddb3bd52fdc92fdc9b12cf3c6d8e0510 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1716244 Commit-Queue: Tim Van Patten <timvp@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>