Build: remove obsolete compiler arguments

These compiler arguments enable features which are enabled by default in
the current Kotlin anyway.

The only exception is in :compiler:cli which uses an old language
version.

compiler/ir/serialization.common/build.gradle.kts

@@ -24,7 +24,6 @@ tasks {
     val compileKotlin by existing(org.jetbrains.kotlin.gradle.tasks.KotlinCompile::class) {
         kotlinOptions {
             freeCompilerArgs += "-Xopt-in=org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI"
-            freeCompilerArgs += "-Xinline-classes"
         }
     }
 }