fix(float): remove -1 in height clamp

Problem: Clamp for height in floating windows enforced no more than
editor height - 1, disallowing full editor height floating windows when
using cmdheight=0

Solution: Clamp to full height, removing the -1. Tested to give the
intended results with cmdheight=0, 1, or more than 1. This also
inadvertently fixes a rendering error with cmdheight >1 where the
bottom border would be overlapped by the cmdline.

src/nvim/window.c

@@ -834,7 +834,7 @@ void win_config_float(win_T *wp, FloatConfig fconfig)
   }
 
   if (!ui_has(kUIMultigrid)) {
-    wp->w_height = MIN(wp->w_height, Rows - 1 - win_border_height(wp));
+    wp->w_height = MIN(wp->w_height, Rows - win_border_height(wp));
     wp->w_width = MIN(wp->w_width, Columns - win_border_width(wp));
   }