[2.x] Remove compilerVersionDependentScalacOptions

[Friendseeker]

This PR removes compilerVersionDependentScalacOptions from build.sbt as Zinc 2.x no longer needs to cross build against Scala 2.

As result a bunch more compiler deprecation warnings are surfaced in CI. For example

[warn] -- Deprecation Warning: /home/runner/work/zinc/zinc/internal/zinc-classpath/src/main/scala/sbt/internal/inc/ReflectUtilities.scala:38:29 
[warn] 38 |  def fields(clazz: Class[?]) =
[warn]    |                             ^
[warn]    |class OpenHashMap in package scala.collection.mutable is deprecated since 2.13.0: Use HashMap or one of the specialized versions (LongMap, AnyRefMap) instead of OpenHashMap

(https://github.com/sbt/zinc/actions/runs/11399506018/job/31718419535)

Is not seen in the latest develop CI run.

Closes #1467

[eed3si9n]

Thanks!