surfaceflinger: remove USE_HWC2

Remove USE_HWC2 and assume it to be true.  Remove all !USE_HWC2
code.

This also fixes a compile error in tests/fakehwc, which never
defines USE_HWC2.

Test: boots taimen and hikey960
Change-Id: Ie6d2fcf884aa6fc715ab0ce19a1e0f7c8acf734c
diff --git a/services/surfaceflinger/tests/fakehwc/FakeComposerClient.h b/services/surfaceflinger/tests/fakehwc/FakeComposerClient.h
index 2a5a8ad..b944182 100644
--- a/services/surfaceflinger/tests/fakehwc/FakeComposerClient.h
+++ b/services/surfaceflinger/tests/fakehwc/FakeComposerClient.h
@@ -16,7 +16,11 @@
 
 #pragma once
 
+#define HWC2_USE_CPP11
+#define HWC2_INCLUDE_STRINGIFICATION
 #include "ComposerClient.h"
+#undef HWC2_USE_CPP11
+#undef HWC2_INCLUDE_STRINGIFICATION
 #include "RenderState.h"
 
 // Needed for display type/ID enums