feat(task): remove warning about being unstable (#16281)

`deno task` has been in use for a few months now. It was very
well received and there are not many complaints. I feel like
this warning might be discouraging for some users and we don't
really plan to make drastic changes to it (besides adding support
for globs in unspecified future).

cli/tests/testdata/task/task_exit_code_5.out

@@ -1,3 +1,2 @@
-Warning deno task is unstable and may drastically change in the future
 Task exit_code_5 echo $(echo 10 ; exit 2) && exit 5
 10

cli/tests/testdata/task/task_non_existent.out

@@ -1,4 +1,3 @@
-Warning deno task is unstable and may drastically change in the future
 Task not found: non_existent
 Available tasks:
 - boolean_logic

cli/tools/task.rs

@@ -25,10 +25,6 @@ pub async fn execute_script(
   flags: Flags,
   task_flags: TaskFlags,
 ) -> Result<i32, AnyError> {
-  log::warn!(
-    "{} deno task is unstable and may drastically change in the future",
-    crate::colors::yellow("Warning"),
-  );
   let ps = ProcState::build(flags).await?;
   let tasks_config = ps.options.resolve_tasks_config()?;
   let config_file_url = ps.options.maybe_config_file_specifier().unwrap();