Remove Subscription Wrapper from Observable.subscribe

Remove Subscription Wrapper from Observable.subscribe

Performance increase from 7.7m to 8.8m ops/second

Before:
```
Benchmark (size) Mode Samples Mean Mean error Units
r.u.PerfTransforms.mapTransformation 1 thrpt 5 7714453.187 362218.633 ops/s
r.u.PerfTransforms.mapTransformation 1 thrpt 5 7527144.767 497816.471 ops/s
```
After:
```
Benchmark (size) Mode Samples Mean Mean error Units
r.u.PerfTransforms.mapTransformation 1 thrpt 5 8853534.333 183494.242 ops/s
r.u.PerfTransforms.mapTransformation 1 thrpt 5 8806958.403 452595.219 ops/s
```

Test can be run  using:

```
../gradlew benchmarks '-Pjmh=-f 1 -tu s -bm thrpt -wi 5 -i 5 -r 5 -prof GC .*PerfTransforms.mapTransformation*'
```