Clean up interface to ProgramImpl::link.

We no longer need to pass mutable shaders with the changed to packed
varyings.

BUG=angleproject:1123

Change-Id: I0a4bbf5d770ff48e10e3de2146840d8987b1e826
Reviewed-on: https://chromium-review.googlesource.com/295194
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/Program.cpp b/src/libANGLE/Program.cpp
index ca58853..75979d5 100644
--- a/src/libANGLE/Program.cpp
+++ b/src/libANGLE/Program.cpp
@@ -312,9 +312,7 @@
 
     linkOutputVariables();
 
-    rx::LinkResult result =
-        mProgram->link(data, mInfoLog, mData.mAttachedFragmentShader, mData.mAttachedVertexShader);
-
+    rx::LinkResult result = mProgram->link(data, mInfoLog);
     if (result.error.isError() || !result.linkSuccess)
     {
         return result.error;