Reuse hash token instead of new primaryTopicToken

Set whether we're in a pipeline in order to determine how to parse the
hash. The error message changes as a result, since the `hash` never
enters the block.

packages/babel-parser/src/tokenizer/index.js

@@ -431,7 +431,7 @@ export default class Tokenizer extends LocationParser {
           )}'`,
         );
       } else {
-        this.finishOp(tt.primaryTopicReference, 1);
+        this.finishOp(tt.hash, 1);
       }
     } else {
       this.raise(

packages/babel-parser/src/tokenizer/state.js

@@ -26,6 +26,7 @@ export default class State {
     this.maybeInArrowParameters = false;
     this.inGenerator = false;
     this.inAsync = false;
+    this.inPipeline = false;
     this.inPropertyName = false;
     this.inType = false;
     this.inClassProperty = false;
@@ -110,6 +111,7 @@ export default class State {
   inGenerator: boolean;
   inMethod: boolean | N.MethodKind;
   inAsync: boolean;
+  inPipeline: boolean;
   inType: boolean;
   noAnonFunctionType: boolean;
   inPropertyName: boolean;

packages/babel-parser/src/tokenizer/types.js

@@ -86,7 +86,6 @@ export const types: { [name: string]: TokenType } = {
   regexp: new TokenType("regexp", { startsExpr }),
   string: new TokenType("string", { startsExpr }),
   name: new TokenType("name", { startsExpr }),
-  primaryTopicReference: new TokenType("#", { startsExpr }),
   eof: new TokenType("eof"),
 
   // Punctuation token types.