remove unused BinMapper::SizeForSpecificBin() (#4643)

Co-authored-by: Nikita Titov <nekit94-12@hotmail.com>

include/LightGBM/bin.h

@@ -160,13 +160,6 @@ class BinMapper {
   void FindBin(double* values, int num_values, size_t total_sample_cnt, int max_bin, int min_data_in_bin, int min_split_data, bool pre_filter, BinType bin_type,
                bool use_missing, bool zero_as_missing, const std::vector<double>& forced_upper_bounds);
 
-  /*!
-  * \brief Use specific number of bin to calculate the size of this class
-  * \param bin The number of bin
-  * \return Size
-  */
-  static int SizeForSpecificBin(int bin);
-
   /*!
   * \brief Serializing this object to buffer
   * \param buffer The destination

src/io/bin.cpp

@@ -519,21 +519,6 @@ namespace LightGBM {
     }
   }
 
-
-  int BinMapper::SizeForSpecificBin(int bin) {
-    int size = 0;
-    size += static_cast<int>(VirtualFileWriter::AlignedSize(sizeof(int)));
-    size +=
-        static_cast<int>(VirtualFileWriter::AlignedSize(sizeof(MissingType)));
-    size += static_cast<int>(VirtualFileWriter::AlignedSize(sizeof(bool)));
-    size += sizeof(double);
-    size += static_cast<int>(VirtualFileWriter::AlignedSize(sizeof(BinType)));
-    size += 2 * sizeof(double);
-    size += bin * sizeof(double);
-    size += static_cast<int>(VirtualFileWriter::AlignedSize(sizeof(uint32_t))) * 2;
-    return size;
-  }
-
   void BinMapper::CopyTo(char * buffer) const {
     std::memcpy(buffer, &num_bin_, sizeof(num_bin_));
     buffer += VirtualFileWriter::AlignedSize(sizeof(num_bin_));