ports: Replace SDL2 with sdl2-compat

There is no need to keep two SDL versions around

ports/sdl12-compat/patches/0002-add-OS_GetExeName.patch

@@ -0,0 +1,21 @@
+diff -ruN sdl12-compat-1.2.76/src/SDL12_compat.c sdl12-compat-1.2.76-banan_os/src/SDL12_compat.c
+--- sdl12-compat-1.2.76/src/SDL12_compat.c	2026-04-04 03:40:25.000000000 +0300
++++ sdl12-compat-1.2.76-banan_os/src/SDL12_compat.c	2026-07-04 09:13:14.105336073 +0300
+@@ -57,7 +57,7 @@
+ #undef snprintf
+ #undef vsnprintf
+ 
+-#ifdef __linux__
++#if defined(__linux__) || defined(__banan_os__)
+ #include <unistd.h> /* for readlink() */
+ #endif
+ 
+@@ -1486,7 +1486,7 @@
+ #endif
+ };
+ 
+-#ifdef __linux__
++#if defined(__linux__) || defined(__banan_os__)
+ static void OS_GetExeName(char *buf, const unsigned maxpath) {
+     int ret;
+     buf[0] = '\0';