Remove unnecessary DeviceUsesClang.

This build function is unnecessary now that GCC is completely
unsupported for Android platform builds. It is similar to
USE_CLANG_PLATFORM_BUILD from the build/make side of things.

Bug: http://b/64032869
Test: Builds
Change-Id: Iddf5f91cc997c337c77a644265cb8dc4e5a915b4

android/config.go

@@ -430,13 +430,6 @@ func (c *config) DeviceName() string {
 	return *c.ProductVariables.DeviceName
 }
 
-func (c *config) DeviceUsesClang() bool {
-	if c.ProductVariables.DeviceUsesClang != nil {
-		return *c.ProductVariables.DeviceUsesClang
-	}
-	return true
-}
-
 func (c *config) ResourceOverlays() []string {
 	if c.ProductVariables.ResourceOverlays == nil {
 		return nil