Remove unused method (#23000)

Author: Andy

src/compiler/types.ts

@@ -5093,14 +5093,7 @@ namespace ts {
         // Otherwise, returns all the diagnostics (global and file associated) in this collection.
         getDiagnostics(fileName?: string): Diagnostic[];
 
-        // Gets a count of how many times this collection has been modified.  This value changes
-        // each time 'add' is called (regardless of whether or not an equivalent diagnostic was
-        // already in the collection).  As such, it can be used as a simple way to tell if any
-        // operation caused diagnostics to be returned by storing and comparing the return value
-        // of this method before/after the operation is performed.
-        getModificationCount(): number;
-
-        /* @internal */ reattachFileDiagnostics(newFile: SourceFile): void;
+        reattachFileDiagnostics(newFile: SourceFile): void;
     }
 
     // SyntaxKind.SyntaxList

src/compiler/utilities.ts

@@ -2557,20 +2557,14 @@ namespace ts {
         const filesWithDiagnostics = [] as SortedArray<string>;
         const fileDiagnostics = createMap<SortedArray<Diagnostic>>();
         let hasReadNonFileDiagnostics = false;
-        let modificationCount = 0;
 
         return {
             add,
             getGlobalDiagnostics,
             getDiagnostics,
-            getModificationCount,
             reattachFileDiagnostics
         };
 
-        function getModificationCount() {
-            return modificationCount;
-        }
-
         function reattachFileDiagnostics(newFile: SourceFile): void {
             forEach(fileDiagnostics.get(newFile.fileName), diagnostic => diagnostic.file = newFile);
         }
@@ -2596,7 +2590,6 @@ namespace ts {
             }
 
             insertSorted(diagnostics, diagnostic, compareDiagnostics);
-            modificationCount++;
         }
 
         function getGlobalDiagnostics(): Diagnostic[] {