Swift: Fix toString on regex literals.

swift/ql/lib/codeql/swift/elements/expr/RegexLiteralExpr.qll

@@ -1,7 +1,5 @@
 private import codeql.swift.generated.expr.RegexLiteralExpr
 
 class RegexLiteralExpr extends Generated::RegexLiteralExpr {
-  override string toString() {
-    result = "..." // TODO: We can improve this once we extract the regex
-  }
+  override string toString() { result = this.getPattern() }
 }