!par strip down shapeless2 to the bare minimum needed

This should bring down compile times and package size quite a bit.

Before:
```
sbt "project akka-parsing-experimental" package  224.23s user 3.58s system 209% cpu 1:48.53 total
2.6M akka-parsing-experimental_2.10-0.6-SNAPSHOT.jar
```

After:
```
sbt "project akka-parsing-experimental" package  124.57s user 2.69s system 190% cpu 1:06.75 total
575K akka-parsing-experimental_2.10-0.6-SNAPSHOT.jar
```


Follow up PR: #15876