Everywhere: Remove unnecessary headers 2/4

Arbitrarily split up to make git bisect easier.

These unnecessary #include's were found by combining an automated tool (which
determined likely candidates) and some brain power (which decided whether
the #include is also semantically superfluous).

AK/IDAllocator.h

@@ -27,7 +27,6 @@
 #pragma once
 
 #include <AK/HashTable.h>
-#include <stdlib.h>
 
 namespace AK {
 

AK/JsonObject.h

@@ -31,7 +31,6 @@
 #include <AK/JsonObjectSerializer.h>
 #include <AK/JsonValue.h>
 #include <AK/String.h>
-#include <AK/StringImpl.h>
 
 namespace AK {
 

AK/LogStream.cpp

@@ -35,10 +35,6 @@
 #    include <Kernel/Thread.h>
 #endif
 
-#if !defined(KERNEL)
-#    include <stdio.h>
-#endif
-
 namespace AK {
 
 const LogStream& operator<<(const LogStream& stream, const String& value)

AK/String.cpp

@@ -34,10 +34,6 @@
 #include <AK/StringView.h>
 #include <AK/Vector.h>
 
-#ifndef KERNEL
-#    include <inttypes.h>
-#endif
-
 namespace AK {
 
 String::String(const StringView& view)