Remove the zero-copy mode

After removing the string size from `VariantContent`, `deserializeJson()` and `deserializeMsgPack()` could not support NUL in strings in the zero-copy mode anymore.
Instead of adding a complicated warning in the documentation, I thought it was better to remove the zero-copy mode entirely.
The zero-copy mode has always been a source of bugs because many users used it without realizing it.
Also, the memory savings are smaller now that we deduplicate strings, so this feature should not be missed much.

src/ArduinoJson/StringStorage/StringMover.hpp

@@ -1,47 +0,0 @@
-// ArduinoJson - https://arduinojson.org
-// Copyright © 2014-2023, Benoit BLANCHON
-// MIT License
-
-#pragma once
-
-#include <ArduinoJson/Namespace.hpp>
-#include <ArduinoJson/Strings/JsonString.hpp>
-
-ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
-
-class StringMover {
- public:
-  StringMover(char* ptr) : writePtr_(ptr) {}
-
-  void startString() {
-    startPtr_ = writePtr_;
-  }
-
-  FORCE_INLINE const char* save() {
-    *writePtr_++ = 0;  // terminator
-    return startPtr_;
-  }
-
-  void append(char c) {
-    *writePtr_++ = c;
-  }
-
-  bool isValid() const {
-    return true;
-  }
-
-  JsonString str() const {
-    writePtr_[0] = 0;  // terminator
-    return JsonString(startPtr_, size(), JsonString::Linked);
-  }
-
-  size_t size() const {
-    return size_t(writePtr_ - startPtr_);
-  }
-
- private:
-  char* writePtr_;
-  char* startPtr_;
-};
-
-ARDUINOJSON_END_PRIVATE_NAMESPACE

src/ArduinoJson/StringStorage/StringStorage.hpp

@@ -5,7 +5,6 @@
 #pragma once
 
 #include <ArduinoJson/StringStorage/StringCopier.hpp>
-#include <ArduinoJson/StringStorage/StringMover.hpp>
 
 ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
 
@@ -15,10 +14,4 @@ StringCopier makeStringStorage(TInput&, MemoryPool* pool) {
   return StringCopier(pool);
 }
 
-template <typename TChar>
-StringMover makeStringStorage(
-    TChar* input, MemoryPool*,
-    typename enable_if<!is_const<TChar>::value>::type* = 0) {
-  return StringMover(reinterpret_cast<char*>(input));
-}
 ARDUINOJSON_END_PRIVATE_NAMESPACE