Remove unused string extension method

Author: plemarquand

Sources/SwiftSyntax/Utils.swift

@@ -120,29 +120,3 @@ extension RawUnexpectedNodesSyntax {
     self.init(raw: raw)
   }
 }
-
-extension String {
-  func trimmingCharacters(in charactersToTrim: any BidirectionalCollection<Character>) -> Substring {
-    let leadingCharacters = countOfSequentialCharacters(charactersToTrim, in: self)
-    let trailingCharacters = countOfSequentialCharacters(charactersToTrim, in: reversed())
-
-    return dropFirst(leadingCharacters).dropLast(trailingCharacters)
-  }
-}
-
-private func countOfSequentialCharacters(
-  _ charactersToCount: any BidirectionalCollection<Character>,
-  in characters: any BidirectionalCollection<Character>
-) -> Int {
-  var count = 0
-
-  for character in characters {
-    if charactersToCount.contains(character) {
-      count += 1
-    } else {
-      break
-    }
-  }
-
-  return count
-}