make k2 default for kotlin library

Summary:
We made it defaut for fb_android_library in the past.
https://fb.workplace.com/groups/androidfyi/permalink/27688974757391110/

Now making it default for kotlin_library.

Reviewed By: navidqar

Differential Revision: D74074441

fbshipit-source-id: bb37f44d3dc12c42ea65c1177b144f0d9e2c1be1

Author: RuslanLa

prelude/kotlin/kotlin_library.bzl

@@ -284,7 +284,7 @@ def get_language_version(ctx: AnalysisContext) -> str:
         if "-language-version" in str(arg):
             current_language_version = str(arg).split("=")[1].strip(' "')
 
-    if ctx.attrs.k2 == True and kotlin_toolchain.allow_k2_usage:
+    if ctx.attrs.k2 != False and kotlin_toolchain.allow_k2_usage:
         if not current_language_version or current_language_version < "2.0":
             if current_kotlin_release_version < "2.0":
                 current_language_version = "2.0"