Kernel: Remove unused variable Thread::m_userspace_stack_region

Kernel/Thread.cpp

@@ -126,9 +126,6 @@ Thread::~Thread()
     if (selector())
         gdt_free_entry(selector());
 
-    if (m_userspace_stack_region)
-        m_process.deallocate_region(*m_userspace_stack_region);
-
     ASSERT(m_process.m_thread_count);
     m_process.m_thread_count--;
 }

Kernel/Thread.h

@@ -424,7 +424,6 @@ private:
     u32 m_signal_mask { 0 };
     u32 m_kernel_stack_base { 0 };
     u32 m_kernel_stack_top { 0 };
-    Region* m_userspace_stack_region { nullptr };
     OwnPtr<Region> m_kernel_stack_region;
     VirtualAddress m_thread_specific_data;
     SignalActionData m_signal_action_data[32];