Remove deprecated functionality

The following deprecated features are no longer supported:
- frag_coord builtin
- sample_mask_in and sample_mask_out builtins
- void keyword
- const keyword

Fixed: tint:677
Fixed: tint:699
Fixed: tint:714
Fixed: tint:715
Change-Id: I40ce9711310e70e62465f58f2a7f4d959039e307
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/52041
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/ast/builtin.cc

@@ -39,10 +39,6 @@ std::ostream& operator<<(std::ostream& out, Builtin builtin) {
       out << "front_facing";
       break;
     }
-    case Builtin::kFragCoord: {
-      out << "frag_coord";
-      break;
-    }
     case Builtin::kFragDepth: {
       out << "frag_depth";
       break;
@@ -71,14 +67,6 @@ std::ostream& operator<<(std::ostream& out, Builtin builtin) {
       out << "sample_mask";
       break;
     }
-    case Builtin::kSampleMaskIn: {
-      out << "sample_mask_in";
-      break;
-    }
-    case Builtin::kSampleMaskOut: {
-      out << "sample_mask_out";
-      break;
-    }
     case Builtin::kPointSize: {
       out << "pointsize";
     }

src/ast/builtin.h

@@ -27,7 +27,6 @@ enum class Builtin {
   kVertexIndex,
   kInstanceIndex,
   kFrontFacing,
-  kFragCoord,  // TODO(crbug.com/tint/714): Remove this
   kFragDepth,
   kLocalInvocationId,
   kLocalInvocationIndex,
@@ -35,8 +34,6 @@ enum class Builtin {
   kWorkgroupId,
   kSampleIndex,
   kSampleMask,
-  kSampleMaskIn,   // TODO(crbug.com/tint/715): Remove this
-  kSampleMaskOut,  // TODO(crbug.com/tint/715): Remove this
 
   // Below are not currently WGSL builtins, but are included in this enum as
   // they are used by certain backends.