Revert "GHOST/wayland: use Wayland only when 'BLENDER_WAYLAND' is set"

This reverts commit c971c851d3.

This change was part of the still-under-review patch D11489, which
hasn't been accepted yet.

intern/ghost/intern/GHOST_ISystem.cpp

@@ -57,13 +57,6 @@ GHOST_TSuccess GHOST_ISystem::createSystem()
     /* Special case, try Wayland, fall back to X11. */
     try {
       m_system = new GHOST_SystemWayland();
-      if (!std::getenv("BLENDER_WAYLAND")) {
-        printf(
-            "Connected to a Wayland compositor but Wayland is disabled at runtime.\n"
-            "Set environment variable 'BLENDER_WAYLAND' "
-            "(e.g. BLENDER_WAYLAND= blender) to use Wayland.\n");
-        throw std::runtime_error(std::string());
-      }
     }
     catch (const std::runtime_error &) {
       /* fallback to X11. */