Fix up lightmapping shader variants.

ScriptableRenderPipeline/LightweightPipeline/LWRP/Shaders/LightweightStandard.shader

 
             // -------------------------------------
             // Unity defined keywords
-            #pragma multi_compile _ DIRLIGHTMAP_COMBINED LIGHTMAP_ON
+            #pragma multi_compile _ DIRLIGHTMAP_COMBINED
+            #pragma multi_compile _ LIGHTMAP_ON
 
             //--------------------------------------
             // GPU Instancing

ScriptableRenderPipeline/LightweightPipeline/LWRP/Shaders/LightweightStandardSimpleLighting.shader

 
             // -------------------------------------
             // Unity defined keywords
-            #pragma multi_compile _ DIRLIGHTMAP_COMBINED LIGHTMAP_ON
+            #pragma multi_compile _ DIRLIGHTMAP_COMBINED
+            #pragma multi_compile _ LIGHTMAP_ON
 
             //--------------------------------------
             // GPU Instancing

ScriptableRenderPipeline/LightweightPipeline/LWRP/Shaders/LightweightStandardTerrain.shader

             #pragma multi_compile _ _VERTEX_LIGHTS
             #pragma multi_compile _ _MIXED_LIGHTING_SUBTRACTIVE
             #pragma multi_compile _ FOG_LINEAR FOG_EXP2
-
+            
-            #pragma multi_compile _ DIRLIGHTMAP_COMBINED LIGHTMAP_ON
+            #pragma multi_compile _ DIRLIGHTMAP_COMBINED
+            #pragma multi_compile _ LIGHTMAP_ON
+
             #pragma multi_compile __ _TERRAIN_NORMAL_MAP
 
             // LW doesn't support dynamic GI. So we save 30% shader variants if we assume