Remove 'errorCode' field from AnalysisError in the analysis server API.

pkg/analysis_server/test/operation/operation_analysis_test.dart

Index: pkg/analysis_server/test/operation/operation_analysis_test.dart
diff --git a/pkg/analysis_server/test/operation/operation_analysis_test.dart b/pkg/analysis_server/test/operation/operation_analysis_test.dart
index c5f5378474ab351b904319413fc08773a55f2a1f..aad71478472f19188e67122040082bd25d2d7de8 100644
--- a/pkg/analysis_server/test/operation/operation_analysis_test.dart
+++ b/pkg/analysis_server/test/operation/operation_analysis_test.dart
@@ -56,7 +56,6 @@ class Test_errorToJson {
   void test_noCorrection() {
     Map<String, Object> json = errorToJson(lineInfo, analysisError);
     expect(json, {
-      ERROR_CODE: 'CompileTimeErrorCode.AMBIGUOUS_EXPORT',
       SEVERITY: 'ERROR',
       TYPE: 'COMPILE_TIME_ERROR',
       LOCATION: {
@@ -73,7 +72,6 @@ class Test_errorToJson {
   void test_noLineInfo() {
     Map<String, Object> json = errorToJson(null, analysisError);
     expect(json, {
-      ERROR_CODE: 'CompileTimeErrorCode.AMBIGUOUS_EXPORT',
       SEVERITY: 'ERROR',
       TYPE: 'COMPILE_TIME_ERROR',
       LOCATION: {
@@ -89,7 +87,6 @@ class Test_errorToJson {
     when(analysisError.correction).thenReturn('my correction');
     Map<String, Object> json = errorToJson(lineInfo, analysisError);
     expect(json, {
-      ERROR_CODE: 'CompileTimeErrorCode.AMBIGUOUS_EXPORT',
       SEVERITY: 'ERROR',
       TYPE: 'COMPILE_TIME_ERROR',
       LOCATION: {