Simplify printSchema directive printing (#3075)

Author: leebyron

src/utilities/printSchema.js

@@ -18,7 +18,7 @@ import type {
   GraphQLInputObjectType,
 } from '../type/definition';
 import { isIntrospectionType } from '../type/introspection';
-import { GraphQLString, isSpecifiedScalarType } from '../type/scalars';
+import { isSpecifiedScalarType } from '../type/scalars';
 import {
   DEFAULT_DEPRECATION_REASON,
   isSpecifiedDirective,
@@ -282,9 +282,9 @@ function printDeprecated(reason: ?string): string {
   if (reason == null) {
     return '';
   }
-  const reasonAST = astFromValue(reason, GraphQLString);
-  if (reasonAST && reason !== DEFAULT_DEPRECATION_REASON) {
-    return ' @deprecated(reason: ' + print(reasonAST) + ')';
+  if (reason !== DEFAULT_DEPRECATION_REASON) {
+    const astValue = print({ kind: 'StringValue', value: reason });
+    return ` @deprecated(reason: ${astValue})`;
   }
   return ' @deprecated';
 }
@@ -293,13 +293,8 @@ function printSpecifiedByURL(scalar: GraphQLScalarType): string {
   if (scalar.specifiedByURL == null) {
     return '';
   }
-  const url = scalar.specifiedByURL;
-  const urlAST = astFromValue(url, GraphQLString);
-  invariant(
-    urlAST,
-    'Unexpected null value returned from `astFromValue` for specifiedByURL',
-  );
-  return ' @specifiedBy(url: ' + print(urlAST) + ')';
+  const astValue = print({ kind: 'StringValue', value: scalar.specifiedByURL });
+  return ` @specifiedBy(url: ${astValue})`;
 }
 
 function printDescription(