Consolidate signal handling

Move the signal handler for SIGCHLD into child-monitor.c
Makes for cleaner code.

kitty/main.py

@@ -4,7 +4,6 @@
 
 import locale
 import os
-import signal
 import sys
 from contextlib import contextmanager
 
@@ -14,8 +13,8 @@ from .cli import create_opts, parse_args
 from .config import cached_values_for, initial_window_size
 from .constants import appname, glfw_path, is_macos, is_wayland, logo_data_file
 from .fast_data_types import (
-    create_os_window, glfw_init, glfw_terminate, install_sigchld_handler,
-    set_default_window_icon, set_options, show_window
+    create_os_window, glfw_init, glfw_terminate, set_default_window_icon,
+    set_options, show_window
 )
 from .fonts.box_drawing import set_scale
 from .utils import (
@@ -152,9 +151,7 @@ def _main():
     try:
         with setup_profiling(args):
             # Avoid needing to launch threads to reap zombies
-            install_sigchld_handler()
             run_app(opts, args)
-            signal.signal(signal.SIGCHLD, signal.SIG_DFL)
     finally:
         glfw_terminate()