gfxstream: nuke set instance for testing

Not used.

BUG=311486792
TEST=compile

Change-Id: Ib81c42b13cb9237fe4605453930d34e857153f6d
diff --git a/guest/platform/VirtGpu.cpp b/guest/platform/VirtGpu.cpp
index 6cb2c58..ac3fd8e 100644
--- a/guest/platform/VirtGpu.cpp
+++ b/guest/platform/VirtGpu.cpp
@@ -45,7 +45,3 @@
         sDevice = nullptr;
     }
 }
-
-void VirtGpuDevice::setInstanceForTesting(VirtGpuDevice* device) {
-    sDevice = device;
-}
diff --git a/guest/platform/include/VirtGpu.h b/guest/platform/include/VirtGpu.h
index b9afbdf..1ced8a5 100644
--- a/guest/platform/include/VirtGpu.h
+++ b/guest/platform/include/VirtGpu.h
@@ -180,8 +180,6 @@
     static VirtGpuDevice* getInstance(enum VirtGpuCapset capset = kCapsetNone);
     static void resetInstance();
 
-    static void setInstanceForTesting(VirtGpuDevice* device);
-
     VirtGpuDevice(enum VirtGpuCapset capset) : mCapset(capset) {}
     virtual ~VirtGpuDevice() {}