Apply suggestions from code review

Co-authored-by: Tom Hvitved <hvitved@github.com>

Author: tamasvajk

csharp/extractor/Semmle.Extraction.CIL/Entities/TypeDefinitionType.cs

@@ -271,7 +271,7 @@ private bool IsSystemEnum(StringHandle typeName, StringHandle namespaceName)
             foreach (var handle in td.GetFields())
             {
                 var field = Cx.MdReader.GetFieldDefinition(handle);
-                if ((field.Attributes & FieldAttributes.Static) != 0)
+                if (field.Attributes.HasFlag(FieldAttributes.Static))
                 {
                     continue;
                 }

csharp/ql/src/semmle/code/cil/Types.qll

@@ -50,8 +50,8 @@ class Enum extends ValueOrRefType {
   override IntegralType getUnderlyingType() {
     cil_enum_underlying_type(this, result)
     or
-    not exists(IntegralType underlying | cil_enum_underlying_type(this, underlying)) and
-    result = any(IntType i)
+    not cil_enum_underlying_type(this, _) and
+    result instanceof IntType
   }
 }