Make PackedVarying a D3D-only type.

The register assignment stuff only applies to the D3D back-end.
Cleans up the GL back-ends use of PackedVarying, and will lead
to future cleanups relating to packing varyings.

BUG=angleproject:1123

Change-Id: Iaaa5fc03577e5b61ea6ae76ee1e15ad608037f34
Reviewed-on: https://chromium-review.googlesource.com/295190
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/Shader.cpp b/src/libANGLE/Shader.cpp
index 27735ec..ad7f674 100644
--- a/src/libANGLE/Shader.cpp
+++ b/src/libANGLE/Shader.cpp
@@ -174,7 +174,7 @@
     return mShader->getShaderVersion();
 }
 
-const std::vector<gl::PackedVarying> &Shader::getVaryings() const
+const std::vector<sh::Varying> &Shader::getVaryings() const
 {
     return mShader->getVaryings();
 }
@@ -199,7 +199,7 @@
     return mShader->getActiveOutputVariables();
 }
 
-std::vector<gl::PackedVarying> &Shader::getVaryings()
+std::vector<sh::Varying> &Shader::getVaryings()
 {
     return mShader->getVaryings();
 }