Gemini parser cleanup

GeminiFormat/GeminiParser.swift

@@ -81,13 +81,6 @@ public struct GeminiParser {
     
 }
 
-fileprivate extension GeminiParser {
-    enum PreformattingState {
-        case off
-        case on(_ alt: String?)
-    }
-}
-
 fileprivate extension String {
     func firstNonWhitespaceIndex(after index: String.Index) -> String.Index {
         var index = index