[v9.5.x] Revert "Prometheus: Reduce allocations parsing exemplars" (#66374)

Revert "Prometheus: Reduce allocations parsing exemplars" (#66367)

Revert "Prometheus: Reduce allocations parsing exemplars (#58959)"

This reverts commit a1f2d0e205.

(cherry picked from commit d830591cdc)

Co-authored-by: Gábor Farkas <gabor.farkas@gmail.com>

pkg/tsdb/prometheus/querydata/framing_bench_test.go

@@ -41,7 +41,6 @@ func BenchmarkExemplarJson(b *testing.B) {
 	tCtx, err := setup(true)
 	require.NoError(b, err)
 	b.ResetTimer()
-	b.ReportAllocs()
 	for n := 0; n < b.N; n++ {
 		res := http.Response{
 			StatusCode: 200,