Remove unused using statements

src/Lucene.Net/Analysis/TokenStreamToAutomaton.cs

@@ -1,9 +1,8 @@
-using J2N;
+using J2N;
 using Lucene.Net.Analysis.TokenAttributes;
 using Lucene.Net.Diagnostics;
 using Lucene.Net.Util;
 using System;
-using System.Diagnostics;
 
 namespace Lucene.Net.Analysis
 {

src/Lucene.Net/Codecs/MappingMultiDocsAndPositionsEnum.cs

@@ -1,5 +1,4 @@
-using Lucene.Net.Support;
-using System;
+using Lucene.Net.Support;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 

src/Lucene.Net/Codecs/MappingMultiDocsEnum.cs

@@ -1,6 +1,5 @@
-using Lucene.Net.Diagnostics;
+using Lucene.Net.Diagnostics;
 using Lucene.Net.Support;
-using System;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 

src/Lucene.Net/Codecs/TermsConsumer.cs

@@ -1,7 +1,6 @@
 using Lucene.Net.Diagnostics;
 using Lucene.Net.Index;
 using System.Collections.Generic;
-using System.Diagnostics;
 using System.Runtime.CompilerServices;
 
 namespace Lucene.Net.Codecs

src/Lucene.Net/Store/BufferedChecksumIndexInput.cs

@@ -1,5 +1,4 @@
 using Lucene.Net.Support;
-using System;
 
 namespace Lucene.Net.Store
 {

src/Lucene.Net/Util/CollectionUtil.cs

@@ -1,5 +1,4 @@
-using J2N.Collections.Generic.Extensions;
-using System;
+using J2N.Collections.Generic.Extensions;
 using System.Collections.Generic;
 using System.Runtime.CompilerServices;