Revert "Always include public/include headers for vulkan and just guard src files with SK_VULKAN."

This reverts commit 6e2d607334cc57c22e3a52179743763828ea84b2.

Reason for revert: chrome roll

Original change's description:
> Always include public/include headers for vulkan and just guard src files with SK_VULKAN.
> 
> This should allow a client to build a skia library that doesn't use vulkan but still
> has all the public headers defined so that they don't have to build two versions of
> their code.
> 
> Bug: chromium:862144
> Change-Id: I0eecbe0bc48123619f217e2cf318eb9a8c77ccb2
> Reviewed-on: https://skia-review.googlesource.com/158661
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Greg Daniel <egdaniel@google.com>

TBR=egdaniel@google.com,bsalomon@google.com,cblume@chromium.org

Change-Id: I76ae6f435333755fa5d546fc1e5999a324b4fd05
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:862144
Reviewed-on: https://skia-review.googlesource.com/c/159000
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/src/gpu/GrDirectContext.cpp b/src/gpu/GrDirectContext.cpp
index 59b984c..14133cd 100644
--- a/src/gpu/GrDirectContext.cpp
+++ b/src/gpu/GrDirectContext.cpp
@@ -147,19 +147,14 @@
     return context;
 }
 
-sk_sp<GrContext> GrContext::MakeVulkan(const GrVkBackendContext& backendContext) {
 #ifdef SK_VULKAN
+sk_sp<GrContext> GrContext::MakeVulkan(const GrVkBackendContext& backendContext) {
     GrContextOptions defaultOptions;
     return MakeVulkan(backendContext, defaultOptions);
-#else
-    return nullptr;
-#endif
 }
 
 sk_sp<GrContext> GrContext::MakeVulkan(const GrVkBackendContext& backendContext,
                                        const GrContextOptions& options) {
-#ifdef SK_VULKAN
-    GrContextOptions defaultOptions;
     sk_sp<GrContext> context(new GrDirectContext(kVulkan_GrBackend));
 
     context->fGpu = GrVkGpu::Make(backendContext, options, context.get());
@@ -172,10 +167,8 @@
         return nullptr;
     }
     return context;
-#else
-    return nullptr;
-#endif
 }
+#endif
 
 #ifdef SK_METAL
 sk_sp<GrContext> GrContext::MakeMetal(void* device, void* queue) {