[tooling] Remove old GDB workarounds

GDB works far better now with QEMU's `-S` flag. No longer does it
complain about changing the target from 32 to 64 bits. Get rid of the
old `waiting` loop and `sleep` call in the GDB config for the kernel.

Tags: debugging

src/kernel/main.cpp

@@ -72,9 +72,6 @@ init_console()
 void
 kernel_main(args::header *header)
 {
-	bool waiting = header && (header->mode == args::mode::debug);
-	while (waiting);
-
 	kutil::assert_set_callback(__kernel_assert);
 	init_console();