Revert "Add SDL_IsTraySupported"

This reverts commit 47d8bdd1c3.

There are runtime reasons why creating a tray can fail, so the correct approach is not to assume that just because a platform supports a tray that trays are available. Instead, you should create a tray at application startup, for the lifetime of the application, and handle failures at that point.

Closes https://github.com/libsdl-org/SDL/pull/13632

src/tray/cocoa/SDL_tray.m

@@ -82,16 +82,6 @@ void SDL_UpdateTrays(void)
 {
 }
 
-bool SDL_IsTraySupported(void)
-{
-    if (!SDL_IsMainThread()) {
-        SDL_SetError("This function should be called on the main thread");
-        return false;
-    }
-
-    return true;
-}
-
 SDL_Tray *SDL_CreateTray(SDL_Surface *icon, const char *tooltip)
 {
     if (!SDL_IsMainThread()) {

src/tray/dummy/SDL_tray.c

@@ -29,11 +29,6 @@ void SDL_UpdateTrays(void)
 {
 }
 
-bool SDL_IsTraySupported(void)
-{
-    return false;
-}
-
 SDL_Tray *SDL_CreateTray(SDL_Surface *icon, const char *tooltip)
 {
     SDL_Unsupported();

src/tray/unix/SDL_tray.c

@@ -240,24 +240,6 @@ void SDL_UpdateTrays(void)
     SDL_UpdateGtk();
 }
 
-bool SDL_IsTraySupported(void)
-{
-    if (!SDL_IsMainThread()) {
-        SDL_SetError("This function should be called on the main thread");
-        return false;
-    }
-
-    static bool has_trays = false;
-    static bool has_been_detected_once = false;
-
-    if (!has_been_detected_once) {
-        has_trays = init_appindicator() && SDL_Gtk_Init();
-        has_been_detected_once = true;
-    }
-
-    return has_trays;
-}
-
 SDL_Tray *SDL_CreateTray(SDL_Surface *icon, const char *tooltip)
 {
     if (!SDL_IsMainThread()) {

src/tray/windows/SDL_tray.c

@@ -216,16 +216,6 @@ void SDL_UpdateTrays(void)
 {
 }
 
-bool SDL_IsTraySupported(void)
-{
-    if (!SDL_IsMainThread()) {
-        SDL_SetError("This function should be called on the main thread");
-        return false;
-    }
-
-    return true;
-}
-
 SDL_Tray *SDL_CreateTray(SDL_Surface *icon, const char *tooltip)
 {
     if (!SDL_IsMainThread()) {