Bury the conditionals from kernel_thread/kernel_execve series

All architectures have
	CONFIG_GENERIC_KERNEL_THREAD
	CONFIG_GENERIC_KERNEL_EXECVE
	__ARCH_WANT_SYS_EXECVE
None of them have __ARCH_WANT_KERNEL_EXECVE and there are only two callers
of kernel_execve() (which is a trivial wrapper for do_execve() now) left.
Kill the conditionals and make both callers use do_execve().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/init/main.c b/init/main.c
index e33e09d..155ac20 100644
--- a/init/main.c
+++ b/init/main.c
@@ -797,7 +797,9 @@
 static int run_init_process(const char *init_filename)
 {
 	argv_init[0] = init_filename;
-	return kernel_execve(init_filename, argv_init, envp_init);
+	return do_execve(init_filename,
+		(const char __user *const __user *)argv_init,
+		(const char __user *const __user *)envp_init);
 }
 
 static void __init kernel_init_freeable(void);