Clean up and consolidate SD-related code (#10831)

Marlin/src/sd/SdBaseFile.cpp

@@ -1055,7 +1055,7 @@ int8_t SdBaseFile::readDir(dir_t* dir, char* longFilename) {
   if (!isDir() || (0x1F & curPosition_)) return -1;
 
   // If we have a longFilename buffer, mark it as invalid.
-  // If long filename is found it will be filled automatically.
+  // If a long filename is found it will be filled automatically.
   if (longFilename) longFilename[0] = '\0';
 
   while (1) {
@@ -1725,8 +1725,4 @@ int16_t SdBaseFile::write(const void* buf, uint16_t nbyte) {
   return -1;
 }
 
-#if ALLOW_DEPRECATED_FUNCTIONS
-  void (*SdBaseFile::oldDateTime_)(uint16_t &date, uint16_t &time) = 0;
-#endif
-
 #endif // SDSUPPORT