Kernel: Use new Thread::previous_mode to track ticks

Author: https://github.com/tomuta
Commit: 33cdc1d2f1
Pull-request: https://github.com/SerenityOS/serenity/pull/5100
Reviewed-by: https://github.com/awesomekling

Kernel/Thread.cpp

@@ -413,9 +413,9 @@ void Thread::finalize_dying_threads()
     }
 }
 
-bool Thread::tick(bool in_kernel)
+bool Thread::tick()
 {
-    if (in_kernel) {
+    if (previous_mode() == PreviousMode::KernelMode) {
         ++m_process->m_ticks_in_kernel;
         ++m_ticks_in_kernel;
     } else {