Avoid lookahead when parsing pipeline

The error message is worse, but it is much more performant.

packages/babylon/src/parser/expression.js

@@ -310,15 +310,6 @@ export default class ExpressionParser extends LValParser {
         const startLoc = this.state.startLoc;
 
         if (op === tt.pipeline) {
-          const lookahead = this.lookahead();
-
-          if (lookahead.type === tt.arrow) {
-            throw this.raise(
-              this.state.start,
-              `Unexpected arrow "=>" after pipeline body; arrow function in pipeline body must be parenthesized`, // eslint-disable-line
-            );
-          }
-
           if (
             this.match(tt.name) &&
             this.state.value === "await" &&

packages/babylon/test/fixtures/experimental/pipeline-operator/arrow-requires-parens/options.json

@@ -1,4 +1,4 @@
 {
   "plugins": ["pipelineOperator"],
-  "throws": "Unexpected arrow \"=>\" after pipeline body; arrow function in pipeline body must be parenthesized (1:6)"
+  "throws": "Unexpected token, expected \";\" (1:8)"
 }