Fix the failing test

The test case, `tests/compute/assoctype-lookup.slang`, had a bug that
the compute shader was trying to use the varying input/output with the
user defined semantics.

This commit removes the user defined semantics, because the compute
shaders cannot use the user defined semantics.

tests/compute/assoctype-lookup.slang

@@ -16,8 +16,8 @@ struct StandardBoneWeightSet : IBoneWeightSet
 {
     struct PackedType
     {
-        uint boneIds : BONEIDS;
-        uint boneWeights : BONEWEIGHTS;
+        uint boneIds;
+        uint boneWeights;
     };
     PackedType field;
 };
@@ -55,4 +55,4 @@ void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
     int inputVal = int(tid);
     int outputVal = test(inputVal);
     gOutputBuffer[tid] = outputVal;
-}
+}