[New IC] Remove "-dontwarn com.google.gson.**" from compiler.pro

This line was added in commit 8c611e0 to allow the
`incremental-compilation-impl` module to use Gson.

This module is no longer using Gson now (only used by its unit tests),
so we can revert that commit.

^KT-52141 Fixed

prepare/compiler/compiler.pro

@@ -38,7 +38,6 @@
 -dontwarn org.jline.builtins.Nano$Buffer
 -dontwarn com.intellij.util.io.TarUtil
 -dontwarn com.intellij.util.io.Compressor$Tar
--dontwarn com.google.gson.**
 
 # Some annotations from intellijCore/annotations.jar are not presented in org.jetbrains.annotations
 -dontwarn org.jetbrains.annotations.*