fix(littlefs): Use VFSImpl::exists() to avoid false error log

Use exists() from VFSImpl base class and avoid using open() to check whether the file exists, because open() will log an error which is confusing, but might be relevant in case a developer uses open() and expects that the file is there.
#7615

Author: BlueAndi

Diff for: libraries/LittleFS/src/LittleFS.cpp

@@ -33,16 +33,10 @@ class LittleFSImpl : public VFSImpl {
 public:
   LittleFSImpl();
   virtual ~LittleFSImpl() {}
-  virtual bool exists(const char *path);
 };
 
 LittleFSImpl::LittleFSImpl() {}
 
-bool LittleFSImpl::exists(const char *path) {
-  File f = open(path, "r", false);
-  return (f == true);
-}
-
 LittleFSFS::LittleFSFS() : FS(FSImplPtr(new LittleFSImpl())), partitionLabel_(NULL) {}
 
 LittleFSFS::~LittleFSFS() {