Fix window icon not working on X11 with 64bits

Apparently on X11 the maximum icon size is 128x128. 256x256 is too
large for the X11 protocol because the X server unserializes the icons
using "unsigned long" which is 64 bits on Linux. So we have to use
64bits per pixel instead of 32, with 32bits padded to 0.

While there I also got rid of the kitty.rgba file replacing it with a
128x128 PNG file.

Fixes #3260

kitty/main.py

@@ -18,7 +18,7 @@ from .conf.utils import BadLine
 from .config import cached_values_for
 from .constants import (
     appname, beam_cursor_data_file, config_dir, glfw_path, is_macos,
-    is_wayland, kitty_exe, logo_data_file, running_in_kitty
+    is_wayland, kitty_exe, logo_png_file, running_in_kitty
 )
 from .fast_data_types import (
     GLFW_IBEAM_CURSOR, create_os_window, free_font_data, glfw_init,
@@ -121,6 +121,12 @@ def get_macos_shortcut_for(opts: OptionsStub, function: str = 'new_os_window') -
     return ans
 
 
+def set_x11_window_icon() -> None:
+    # max icon size on X11 64bits is 128x128
+    path = logo_png_file.replace('.', '-128.')
+    set_default_window_icon(path)
+
+
 def _run_app(opts: OptionsStub, args: CLIOptions, bad_lines: Sequence[BadLine] = ()) -> None:
     global_shortcuts: Dict[str, SingleKey] = {}
     if is_macos:
@@ -131,8 +137,7 @@ def _run_app(opts: OptionsStub, args: CLIOptions, bad_lines: Sequence[BadLine] =
     if is_macos and opts.macos_custom_beam_cursor:
         set_custom_ibeam_cursor()
     if not is_wayland() and not is_macos:  # no window icons on wayland
-        with open(logo_data_file, 'rb') as f:
-            set_default_window_icon(f.read(), 256, 256)
+        set_x11_window_icon()
     load_shader_programs.use_selection_fg = opts.selection_foreground is not None
     with cached_values_for(run_app.cached_values_name) as cached_values:
         with startup_notification_handler(extra_callback=run_app.first_window_callback) as pre_show_callback: