[PERF] Regex: stop calling Simplify

It slows down compilation and doesn't make any of our benchmarks go faster.
Assumed to be something that helped at an earlier point, but doesn't help now.

Add a benchmark with a more complicated regex to demonstrate the slowdown.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

model/labels/matcher_test.go

@@ -225,6 +225,13 @@ func BenchmarkNewMatcher(b *testing.B) {
 			NewMatcher(MatchRegexp, "foo", "bar")
 		}
 	})
+	b.Run("complex regex", func(b *testing.B) {
+		b.ReportAllocs()
+		b.ResetTimer()
+		for i := 0; i <= b.N; i++ {
+			NewMatcher(MatchRegexp, "foo", "((.*)(bar|b|buzz)(.+)|foo){10}")
+		}
+	})
 }
 
 func BenchmarkMatcher_String(b *testing.B) {

model/labels/regexp.go

@@ -67,8 +67,6 @@ func NewFastRegexMatcher(v string) (*FastRegexMatcher, error) {
 		if err != nil {
 			return nil, err
 		}
-		// Simplify the syntax tree to run faster.
-		parsed = parsed.Simplify()
 		m.re, err = regexp.Compile("^(?s:" + parsed.String() + ")$")
 		if err != nil {
 			return nil, err