Revert of Enable viewer in non-Vulkan builds (patchset #2 id:20001 of https://codereview.chromium.org/2067023002/ )

Reason for revert:
breaking compile bots

Original issue's description:
> Enable viewer in non-Vulkan builds
>
> BUG=skia:
> GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2067023002
>
> Committed: https://skia.googlesource.com/skia/+/746b792a9aad1230ab69158a51c49b2e5437d95b

TBR=djsollen@google.com,jvanverth@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review-Url: https://codereview.chromium.org/2072563002
diff --git a/tools/viewer/Viewer.cpp b/tools/viewer/Viewer.cpp
index f44e1aa..7052a3a 100644
--- a/tools/viewer/Viewer.cpp
+++ b/tools/viewer/Viewer.cpp
@@ -66,9 +66,7 @@
 
 const char *kBackendTypeStrings[sk_app::Window::kBackendTypeCount] = {
     " [OpenGL]",
-#ifdef SK_VULKAN
     " [Vulkan]",
-#endif
     " [Raster]"
 };
 
@@ -88,7 +86,7 @@
     : fCurrentMeasurement(0)
     , fDisplayStats(false)
     , fSplitScreen(false)
-    , fBackendType(sk_app::Window::kNativeGL_BackendType)
+    , fBackendType(sk_app::Window::kVulkan_BackendType)
     , fZoomCenterX(0.0f)
     , fZoomCenterY(0.0f)
     , fZoomLevel(0.0f)
@@ -104,10 +102,9 @@
 
     SkCommandLineFlags::Parse(argc, argv);
 
-#ifdef SK_VULKAN
     fBackendType = FLAGS_vulkan ? sk_app::Window::kVulkan_BackendType
                                 : sk_app::Window::kNativeGL_BackendType;
-#endif
+
     fWindow = Window::CreateNativeWindow(platformData);
     fWindow->attach(fBackendType, DisplayParams());