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

include/SDL3/SDL_tray.h

@@ -96,25 +96,6 @@ typedef Uint32 SDL_TrayEntryFlags;
  */
 typedef void (SDLCALL *SDL_TrayCallback)(void *userdata, SDL_TrayEntry *entry);
 
-/**
- * Check whether or not tray icons can be created.
- *
- * Note that this function does not guarantee that SDL_CreateTray() will or
- * will not work; you should still check SDL_CreateTray() for errors.
- *
- * Using tray icons require the video subsystem.
- *
- * \returns true if trays are available, false otherwise.
- *
- * \threadsafety This function should only be called on the main thread. It
- *               will return false if not called on the main thread.
- *
- * \since This function is available since SDL 3.4.0.
- *
- * \sa SDL_CreateTray
- */
-extern SDL_DECLSPEC bool SDLCALL SDL_IsTraySupported(void);
-
 /**
  * Create an icon to be placed in the operating system's tray, or equivalent.
  *