Remove invalid async-flag from syntax error tests (#959)

src/params/syntax/async-gen-named-func-expr.template

@@ -13,7 +13,6 @@ info: |
         7. Let closure be ! AsyncGeneratorFunctionCreate(Normal, FormalParameters,
            AsyncGeneratorBody, funcEnv, strict).
         [...]
-flags: [async]
 features: [async-iteration]
 ---*/
 

test/language/expressions/async-generator/params-named-dflt-duplicates.js

@@ -5,7 +5,7 @@
 description: It is a Syntax Error if BoundNames of FormalParameters contains any duplicate elements. (async generator named function expression)
 esid: sec-asyncgenerator-definitions-evaluation
 features: [default-parameters, async-iteration]
-flags: [generated, async]
+flags: [generated]
 negative:
   phase: early
   type: SyntaxError

test/language/expressions/async-generator/params-named-dflt-rest.js

@@ -5,7 +5,7 @@
 description: RestParameter does not support an initializer (async generator named function expression)
 esid: sec-asyncgenerator-definitions-evaluation
 features: [default-parameters, async-iteration]
-flags: [generated, async]
+flags: [generated]
 negative:
   phase: early
   type: SyntaxError

test/language/expressions/async-generator/params-named-trailing-comma-rest-early-error.js

@@ -5,7 +5,7 @@
 description: It's a syntax error if a FunctionRestParameter is followed by a trailing comma (async generator named function expression)
 esid: sec-asyncgenerator-definitions-evaluation
 features: [async-iteration]
-flags: [generated, async]
+flags: [generated]
 negative:
   phase: early
   type: SyntaxError