Do not use dev Kotlin version

[irenedea]

We were using the Kotlin dev version because shapeTyping is dependent on some compiler changes that are not released in the main build yet.

This issue should be addressed when our changes are in the main build for Kotlin. I believe this should be in the 1.7.0 release (currently latest the Kotlin version is 1.6.21)

There are two things to do:

1. Update the Kotlin version to a non dev version from MavenCentral
2. Remove dependency to the kotlin bootstrap maven repository

maven repository dependency:
https://github.com/facebookresearch/diffkt/blob/main/kotlin/build.gradle.kts#L41
https://github.com/facebookresearch/diffkt/blob/main/kotlin/settings.gradle.kts#L32

Kotlin version is declared here: https://github.com/facebookresearch/diffkt/blob/main/kotlin/gradle.properties#L9