popup: one text drawing call; drop what the draw thread never reaches

font.c exported three wrappers for one function, and the fit == -1 mode
existed only for the tests; textdraw() takes fit and colour. win.c
tested the empty picture in the thread and again in winshow, interned
two atoms by hand next to getatom(), kept a consumer-side drain that the
producer's already guarantees never finds anything, zeroed ten globals
before returning from the only thread that read them, and re-checked
sizes that resizebacking had just established. The page marker is laid
out once and drawn from the layout instead of being recomputed.

fn.h

@@ -47,6 +47,4 @@ void*	erealloc(void*, ulong);
 int	textinit(void);
 void	textclose(void);
 int	textwidth(Str*);
-void	textdraw(u32int*, int, int, int, int, Str*);
-void	textdrawfit(u32int*, int, int, int, int, int, Str*);
-void	textdrawfitcolor(u32int*, int, int, int, int, int, u32int, Str*);
+void	textdraw(u32int*, int, int, int, int, int, u32int, Str*);