Delete src/thread/n3ds/SDL_syscond.c

This PR removes the incorrect implementation of `SDL_cond` currently included with the 3DS port.

Pseudocode of the incorrect implementation of `SDL_CondWait` this PR removes:

* Receive an `SDL_cond` backed by a `libctru` `CondVar` and an `SDL_mutex` backed by a `libctru` `RecursiveLock`.
* Want to call `libctru` function `CondVar_Wait` which expects a `CondVar` and a `LightLock` (non-recursive lock)
* Do so by calling this function with the internal (inadequately protected) `LightLock` member of the `RecursiveLock` (`&mutex->lock.lock` on line 105), without updating any internal thread or lock count fields of the `RecursiveLock`.

Happy to discuss or test some examples. My own use case works much better with the generic cond logic, and this seems like a safe fix to me given that the generic logic is well-tested and this seems not to be.

If you like the PR I'll send another one for the SDL2 branch.

src/thread/n3ds/SDL_syscond.c

@@ -1,111 +0,0 @@
-/*
-  Simple DirectMedia Layer
-  Copyright (C) 1997-2025 Sam Lantinga <slouken@libsdl.org>
-
-  This software is provided 'as-is', without any express or implied
-  warranty.  In no event will the authors be held liable for any damages
-  arising from the use of this software.
-
-  Permission is granted to anyone to use this software for any purpose,
-  including commercial applications, and to alter it and redistribute it
-  freely, subject to the following restrictions:
-
-  1. The origin of this software must not be misrepresented; you must not
-     claim that you wrote the original software. If you use this software
-     in a product, an acknowledgment in the product documentation would be
-     appreciated but is not required.
-  2. Altered source versions must be plainly marked as such, and must not be
-     misrepresented as being the original software.
-  3. This notice may not be removed or altered from any source distribution.
-*/
-#include "SDL_internal.h"
-
-#ifdef SDL_THREAD_N3DS
-
-// An implementation of condition variables using libctru's CondVar
-
-#include "SDL_sysmutex_c.h"
-
-struct SDL_Condition
-{
-    CondVar cond_variable;
-};
-
-// Create a condition variable
-SDL_Condition *SDL_CreateCondition(void)
-{
-    SDL_Condition *cond = (SDL_Condition *)SDL_malloc(sizeof(SDL_Condition));
-    if (cond) {
-        CondVar_Init(&cond->cond_variable);
-    }
-    return cond;
-}
-
-// Destroy a condition variable
-void SDL_DestroyCondition(SDL_Condition *cond)
-{
-    if (cond) {
-        SDL_free(cond);
-    }
-}
-
-// Restart one of the threads that are waiting on the condition variable
-void SDL_SignalCondition(SDL_Condition *cond)
-{
-    if (!cond) {
-        return;
-    }
-
-    CondVar_Signal(&cond->cond_variable);
-}
-
-// Restart all threads that are waiting on the condition variable
-void SDL_BroadcastCondition(SDL_Condition *cond)
-{
-    if (!cond) {
-        return;
-    }
-
-    CondVar_Broadcast(&cond->cond_variable);
-}
-
-/* Wait on the condition variable for at most 'timeoutNS' nanoseconds.
-   The mutex must be locked before entering this function!
-   The mutex is unlocked during the wait, and locked again after the wait.
-
-Typical use:
-
-Thread A:
-    SDL_LockMutex(lock);
-    while ( ! condition ) {
-        SDL_WaitCondition(cond, lock);
-    }
-    SDL_UnlockMutex(lock);
-
-Thread B:
-    SDL_LockMutex(lock);
-    ...
-    condition = true;
-    ...
-    SDL_SignalCondition(cond);
-    SDL_UnlockMutex(lock);
- */
-bool SDL_WaitConditionTimeoutNS(SDL_Condition *cond, SDL_Mutex *mutex, Sint64 timeoutNS)
-{
-    Result res;
-
-    if (!cond || !mutex) {
-        return true;
-    }
-
-    res = 0;
-    if (timeoutNS < 0) {
-        CondVar_Wait(&cond->cond_variable, &mutex->lock.lock);
-    } else {
-        res = CondVar_WaitTimeout(&cond->cond_variable, &mutex->lock.lock, timeoutNS);
-    }
-
-    return R_SUCCEEDED(res);
-}
-
-#endif // SDL_THREAD_N3DS