Remove support for moshi-reflective approach

[macisamuele]

PR #82 has added support for code-generated Moshi Adapters.
As result of the discussion on the PR we need clear up the current mixed support of reflective and moshi-codegen approach.

We need to do it in order to:

• reduce complexity
• reduce dependencies (as mentioned in Add support for moshi-kotlin-codegen #62 moshi-kotlin depends on kotlin-reflect which is pretty big)
• provide better performances with the least surprises for user

In order to achieve such objective we need to:

• Remove kotlin-android-with-moshi-kotlin-codegen and update kotlin-android to use only moshi-kotlin-codegen
• Update groovy-android
• Improve documentation to highlight a possible approach to still use reflective approach (a way to rebuild GeneratedCodeConverters.moshi)

Disclaimer: The list is not supposed to be complete, so if I'm missing something please update the checklist ;)

[cortinico]

As a side note: it's probably worth to investigate a bit around https://github.com/Kotlin/kotlinx.reflect.lite