Remove redundant ProgramVariant feature because it got deprecated.

Signed-off-by: Yaakuro <y1@codeposer.net>

Gems/Atom/Feature/Common/Assets/Shaders/PostProcessing/MSAAResolveCustom.shader

@@ -18,7 +18,5 @@
           "type": "Fragment"
         }
       ]
-    },
-
-    "ProgramVariants": []
+    }
 }

Gems/Atom/Feature/Common/Assets/Shaders/Reflections/ReflectionScreenSpaceBlurHorizontal.shader

@@ -29,8 +29,5 @@
                 "type": "Fragment"
             }
         ]
-    },
-
-    "ProgramVariants": [
-    ]
+    }
 }

Gems/Atom/Feature/Common/Assets/Shaders/Reflections/ReflectionScreenSpaceBlurVertical.shader

@@ -30,8 +30,5 @@
                 "type": "Fragment"
             }
         ]
-    },
-
-    "ProgramVariants": [
-    ]
+    }
 }

Gems/Atom/Feature/Common/Assets/Shaders/Reflections/ReflectionScreenSpaceComposite.shader

@@ -37,8 +37,5 @@
                 "type": "Fragment"
             }
         ]
-    },
-
-    "ProgramVariants": [
-    ]
+    }
 }

Gems/Atom/Feature/Common/Assets/Shaders/Reflections/ReflectionScreenSpaceTrace.shader

@@ -30,8 +30,5 @@
                 "type": "Fragment"
             }
         ]
-    },
-
-    "ProgramVariants": [
-    ]
+    }
 }