plot: remove unused windowbase field

src/lib/internal.h

@@ -156,8 +156,9 @@ typedef struct ncplot {
   uint64_t minchannel;
   bool vertical_indep;
   ncgridgeom_e gridtype;
-  int64_t windowbase; // first valid x value
-  uint64_t rangex; // windowbase + rangex - 1 -> last valid x
+  // requested number of slots. 0 for automatically setting the number of slots
+  // to span the horizontal area.
+  uint64_t rangex;
   // domain minimum and maximum. if detectdomain is true, these are
   // progressively enlarged/shrunk to fit the sample set. if not, samples
   // outside these bounds are counted, but the displayed range covers only this.

src/lib/plot.c

@@ -124,7 +124,6 @@ ncplot* ncplot_create(ncplane* n, const ncplot_options* opts){
         ret->maxy = 0;
         ret->miny = ~(uint64_t)0ull;
       }
-      ret->windowbase = 0;
       ret->slotstart = 0;
       ret->slotx = 0;
       redraw_plot(ret);