gfxstream: nuke set instance for testing

Not used.

Reviewed-by: Aaron Ruby <aruby@blackberry.com>
Acked-by: Yonggang Luo <luoyonggang@gmail.com>
Acked-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27246>

src/gfxstream/guest/platform/VirtGpu.cpp

@@ -45,7 +45,3 @@ void VirtGpuDevice::resetInstance() {
         sDevice = nullptr;
     }
 }
-
-void VirtGpuDevice::setInstanceForTesting(VirtGpuDevice* device) {
-    sDevice = device;
-}

src/gfxstream/guest/platform/include/VirtGpu.h

@@ -180,8 +180,6 @@ class VirtGpuDevice {
     static VirtGpuDevice* getInstance(enum VirtGpuCapset capset = kCapsetNone);
     static void resetInstance();
 
-    static void setInstanceForTesting(VirtGpuDevice* device);
-
     VirtGpuDevice(enum VirtGpuCapset capset) : mCapset(capset) {}
     virtual ~VirtGpuDevice() {}