Fix derivatives being related to an extension on ESSL3

dFdx, dFdy and fwidth are parts of the core language in ESSL3.

This fixes a regression from the patch "Set symbol extension at insertion".

BUG=angle:926

Change-Id: I6c0bbce3afad1f064ff115a16e23ea79bd584e49
Reviewed-on: https://chromium-review.googlesource.com/255450
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>
diff --git a/src/compiler/translator/Initialize.cpp b/src/compiler/translator/Initialize.cpp
index f953cc5..6c87c61 100644
--- a/src/compiler/translator/Initialize.cpp
+++ b/src/compiler/translator/Initialize.cpp
@@ -352,9 +352,9 @@
 
     if (type == GL_FRAGMENT_SHADER)
     {
-        symbolTable.insertBuiltIn(ESSL3_BUILTINS, EOpDFdx, "GL_OES_standard_derivatives", genType, "dFdx", genType);
-        symbolTable.insertBuiltIn(ESSL3_BUILTINS, EOpDFdy, "GL_OES_standard_derivatives", genType, "dFdy", genType);
-        symbolTable.insertBuiltIn(ESSL3_BUILTINS, EOpFwidth, "GL_OES_standard_derivatives", genType, "fwidth", genType);
+        symbolTable.insertBuiltIn(ESSL3_BUILTINS, EOpDFdx, genType, "dFdx", genType);
+        symbolTable.insertBuiltIn(ESSL3_BUILTINS, EOpDFdy, genType, "dFdy", genType);
+        symbolTable.insertBuiltIn(ESSL3_BUILTINS, EOpFwidth, genType, "fwidth", genType);
     }
 
     symbolTable.insertBuiltIn(ESSL3_BUILTINS, gvec4, "textureOffset", gsampler2D, float2, int2);