Kernel: Remove special-casing of sys$gettid() in syscall entry

We had a fast-path for the gettid syscall that was useful before
we started caching the thread ID in LibC. Just get rid of it. :^)

Kernel/Syscall.cpp

@@ -125,15 +125,7 @@ int handle(RegisterState& regs, u32 function, u32 arg1, u32 arg2, u32 arg3)
 void syscall_handler(TrapFrame* trap)
 {
  auto& regs = *trap->regs;
- // Special handling of the "gettid" syscall since it's extremely hot.
- // FIXME: Remove this hack once userspace locks stop calling it so damn much.
  auto current_thread = Thread::current();
- auto& process = current_thread->process();
- if (regs.eax == SC_gettid) {
- regs.eax = process.sys$gettid();
- current_thread->did_syscall();
- return;
- }
 
  if (current_thread->tracer() && current_thread->tracer()->is_tracing_syscalls()) {
  current_thread->tracer()->set_trace_syscalls(false);
@@ -149,6 +141,7 @@ void syscall_handler(TrapFrame* trap)
  asm volatile(""
  : "=m"(*ptr));
 
+ auto& process = current_thread->process();
  if (!MM.validate_user_stack(process, VirtualAddress(regs.userspace_esp))) {
  dbg() << "Invalid stack pointer: " << String::format("%p", regs.userspace_esp);
  handle_crash(regs, "Bad stack on syscall entry", SIGSTKFLT);