Stop overriding the image capability to true in BlimpContextProvider.

It should be true if the GL context supports it, and off otherwise.
Lying isn't helpful.

It was added in the initial blimp/ commit, without discussion about
why it was there, though it was at least considered as it came up
here: https://chromiumcodereview.appspot.com/1295243003/diff/20001/blimp/client/compositor/blimp_context_provider.cc?_ga=1.66997032.780449993.1417466767#newcode101

R=dtrainor@chromium.org
BUG=584497

Review URL: https://codereview.chromium.org/1898983003

Cr-Commit-Position: refs/heads/master@{#388580}

blimp/client/feature/compositor/blimp_context_provider.cc

@@ -65,12 +65,7 @@ void BlimpContextProvider::DetachFromThread() {
 
 gpu::Capabilities BlimpContextProvider::ContextCapabilities() {
   DCHECK(context_thread_checker_.CalledOnValidThread());
-  gpu::Capabilities capabilities =
-      context_->GetImplementation()->capabilities();
-  // TODO(danakj): Why? Is this even valid? This is the CHROMIUM_image extension
-  // to use GpuMemoryBuffers. Does the context not provide this?
-  capabilities.image = true;
-  return capabilities;
+  return context_->GetImplementation()->capabilities();
 }
 
 gpu::gles2::GLES2Interface* BlimpContextProvider::ContextGL() {