[benchmark] Revert bigger name change

To avoid the need to mess with `lit` tests due to renamed benchmark, let's just add the customary suffix `2` for the bugfixed version. We'll fight the renaming battle another day...

Author: palimondo

benchmark/single-source/RomanNumbers.swift

@@ -21,7 +21,7 @@ let N = 270
 
 public let RomanNumbers = [
   BenchmarkInfo(
-    name: "Roman.Substring.startsWith.dropFirst",
+    name: "RomanNumbers2",
     runFunction: {
       checkId($0, upTo: N, { $0.romanNumeral }, Int.init(romanSSsWdF:)) },
     tags: t),