The test MipmapTest.TextureCubeGeneralLevelZero/ES2_VULKAN was disabled
for Vulkan Android due to Nexus 5x and Pixel 2 issues.   The Nexus 5x
has been removed from the test infrastructure and the Pixel 2 issue
seems to have sorted itself out.

Bug: angleproject:2817
Test: angle_end2end_tests MipmapTest.TextureCubeGeneralLevelZero/ES2_VULKAN
Change-Id: I85bb56707def2906194c34942fcd74a811255abc
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1558293Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Tim Van Patten <timvp@google.com>