Removed SDL_bool in favor of plain bool

We require stdbool.h in the build environment, so we might as well use the plain bool type.

If your environment doesn't have stdbool.h, this simple replacement will suffice:
typedef signed char bool;

test/testtime.c

@@ -46,7 +46,7 @@ static void RenderDateTime(SDL_Renderer *r)
 
     /* Query the current time and print it. */
     SDL_GetCurrentTime(&ticks);
-    SDL_TimeToDateTime(ticks, &dt, SDL_FALSE);
+    SDL_TimeToDateTime(ticks, &dt, false);
 
     switch (date_format) {
     case SDL_DATE_FORMAT_YYYYMMDD:
@@ -78,7 +78,7 @@ static void RenderDateTime(SDL_Renderer *r)
 
     SDLTest_DrawString(r, 10, 15, str);
 
-    SDL_TimeToDateTime(ticks, &dt, SDL_TRUE);
+    SDL_TimeToDateTime(ticks, &dt, true);
     if (time_format) {
         if (dt.hour > 12) { /* PM */
             dt.hour -= 12;