[sixel] kill unused preprocess_cell()

src/lib/sixel.c

@@ -723,18 +723,6 @@ build_data_table(qstate* qs, uint32_t colors, sixeltable* stab, const uint32_t*
   return 0;
 }
 
-// handle a cell's worth of pixels--update its entry in the rmatrix, update
-// its entry in the TAM, update the p2 value if appropriate, update any
-// relevant auxvecs, and add all colors to the decatrees. we are operating
-// on celly and cellx of the image.
-static inline int
-preprocess_cell(const uint32_t* data, int linesize, int cols, int leny,
-                int lenx, sixeltable* stab, tament* tam,
-                int celly, int cellx, const blitterargs* bargs){
-  // FIXME
-  return 0;
-}
-
 // we have a 4096-element array that takes the 4-5-3 MSBs from the RGB
 // comoponents. once it's complete, we might need to either merge some
 // chunks, or expand them, converging towards the available number of