Remove the syscall sandbox

After initially being merged in #20487, it's no-longer clear that an
internal syscall sandboxing mechanism is something that Bitcoin Core
should have/maintain, especially when compared to better
maintained/supported alterantives, i.e firejail.

Note that given where it's used, the sandbox also gets dragged into the
kernel.

There is some related discussion in #24771.

This should not require any sort of deprecation, as this was only ever
an opt-in, experimental feature.

Closes #24771.

src/torcontrol.cpp

@@ -16,7 +16,6 @@
 #include <netbase.h>
 #include <util/readwritefile.h>
 #include <util/strencodings.h>
-#include <util/syscall_sandbox.h>
 #include <util/thread.h>
 #include <util/time.h>
 
@@ -653,7 +652,6 @@ static std::thread torControlThread;
 
 static void TorControlThread(CService onion_service_target)
 {
-    SetSyscallSandboxPolicy(SyscallSandboxPolicy::TOR_CONTROL);
     TorController ctrl(gBase, gArgs.GetArg("-torcontrol", DEFAULT_TOR_CONTROL), onion_service_target);
 
     event_base_dispatch(gBase);