apprt/gtk: remove gtk-gsk-renderer config

This was a hack, and is no longer required since #6877. Users can
explicitly override the GTK GSK renderer by setting the standard GTK env
var `GSK_RENDERER`.

src/apprt/gtk/App.zig

@@ -247,19 +247,6 @@ pub fn init(core_app: *CoreApp, opts: Options) !App {
         _ = internal_os.setenv("GDK_DISABLE", value[0 .. value.len - 1 :0]);
     }
 
-    if (gtk_version.runtimeAtLeast(4, 14, 0)) {
-        switch (config.@"gtk-gsk-renderer") {
-            .default => {},
-            else => |renderer| {
-                // Force the GSK renderer to a specific value. After GTK 4.14 the
-                // `ngl` renderer is used by default which causes artifacts when
-                // used with Ghostty so it should be avoided.
-                log.warn("setting GSK_RENDERER={s}", .{@tagName(renderer)});
-                _ = internal_os.setenv("GSK_RENDERER", @tagName(renderer));
-            },
-        }
-    }
-
     adw.init();
 
     const display: *gdk.Display = gdk.Display.getDefault() orelse {

src/config/Config.zig

@@ -2186,14 +2186,6 @@ keybind: Keybinds = .{},
 /// debug builds, `false` for all others.
 @"gtk-opengl-debug": bool = builtin.mode == .Debug,
 
-/// After GTK 4.14.0, we need to force the GSK renderer to OpenGL as the default
-/// GSK renderer is broken on some systems. If you would like to override
-/// that bekavior, set `gtk-gsk-renderer=default` and either use your system's
-/// default GSK renderer, or set the GSK_RENDERER environment variable to your
-/// renderer of choice before launching Ghostty. This setting has no effect when
-/// using versions of GTK earlier than 4.14.0.
-@"gtk-gsk-renderer": GtkGskRenderer = .opengl,
-
 /// If `true`, the Ghostty GTK application will run in single-instance mode:
 /// each new `ghostty` process launched will result in a new window if there is
 /// already a running process.
@@ -6499,12 +6491,6 @@ pub const WindowPadding = struct {
     }
 };
 
-/// See the `gtk-gsk-renderer` config.
-pub const GtkGskRenderer = enum {
-    default,
-    opengl,
-};
-
 test "parse duration" {
     inline for (Duration.units) |unit| {
         var buf: [16]u8 = undefined;