Kernel: Remove the two remaining ARCH(I386) checks

Author: https://github.com/awesomekling
Commit: d6fa42dd5c
Pull-request: https://github.com/SerenityOS/serenity/pull/15467
Issue: https://github.com/SerenityOS/serenity/issues/15444
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/Hendiadyoin1
Reviewed-by: https://github.com/fuel-pcbox
Reviewed-by: https://github.com/supercomputer7

Kernel/Thread.cpp

@@ -1205,12 +1205,10 @@ DispatchSignalResult Thread::dispatch_signal(u8 signal)
     auto signal_trampoline_addr = process.signal_trampoline().get();
     regs.set_ip(signal_trampoline_addr);
 
+#if ARCH(X86_64)
     // Userspace flags might be invalid for function entry, according to SYSV ABI (section 3.2.1).
     // Set them to a known-good value to avoid weird handler misbehavior.
     // Only IF (and the reserved bit 1) are set.
-#if ARCH(I386)
-    regs.set_flags(2 | (regs.eflags & ~safe_eflags_mask));
-#elif ARCH(X86_64)
     regs.set_flags(2 | (regs.rflags & ~safe_eflags_mask));
 #endif