gfxstream: remove unused imports
gfxstream: remove unused imports

Test: build
Change-Id: I872d3e2b7450a4709a126c774ee82c5e46134e6c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3569544
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Auto-Submit: Kaiyi Li <f6fa95ef69f95b15c9d6b9a996e5e7cbcfb76e84@google.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm