Userland: Remove "Inspector" program and related utilities

This program has never lived up to its original idea, and has been
broken for years (property editing, etc). It's also unmaintained and
off-by-default since forever.

At this point, Inspector is more of a maintenance burden than a feature,
so this commit removes it from the system, along with the mechanism in
Core::EventLoop that enables it.

If we decide we want the feature again in the future, it can be
reimplemented better. :^)

Userland/Applications/SystemMonitor/main.cpp

@@ -263,7 +263,6 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
         return result.release_error();
 
     TRY(Core::System::unveil("/bin/Profiler", "rx"));
-    TRY(Core::System::unveil("/bin/Inspector", "rx"));
     TRY(Core::System::unveil("/bin/HackStudio", "rx"));
     TRY(Core::System::unveil(nullptr, nullptr));