Remove two outdated test inputs from regex match timeout tests (#106174)

Author: stephentoub

src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/Regex.Match.Tests.cs

@@ -1264,8 +1264,6 @@ public static IEnumerable<object[]> Match_Timeout_Throws_MemberData()
                 // Lookarounds
                 yield return new object[] { engine, @"((?=(?>a*))a)+", a1_000_000 };
                 yield return new object[] { engine, @"((?<=(?>a*))a)+", a1_000_000 };
-                yield return new object[] { engine, @"((?!(?>[^a]*))a)+", a1_000_000 };
-                yield return new object[] { engine, @"((?<!(?>[^a]*))a)+", a1_000_000 };
 
                 // All of the below tests have catastrophic backtracking...