Remove superfluous cleanup parameter in os::exit and os::fastexit.

lib/std/os/os.c3

@@ -4,7 +4,7 @@ import libc;
 <*
  Exit the process with a given exit code. This will typically call 'exit' in LibC
 *>
-fn void exit(int result, bool cleanup = true) @weak @noreturn
+fn void exit(int result) @weak @noreturn
 {
 	$if env::LIBC:
 		libc::exit(result);
@@ -17,7 +17,7 @@ fn void exit(int result, bool cleanup = true) @weak @noreturn
  Exit the process with a given exit code. This will typically call '_Exit' in LibC
  usually bypassing '@finalizer' functions.
 *>
-fn void fastexit(int result, bool cleanup = true) @weak @noreturn
+fn void fastexit(int result) @weak @noreturn
 {
 	$if env::LIBC:
 		libc::_exit(result);

releasenotes.md

@@ -51,6 +51,7 @@
 - Add `DateTime + Duration` overloads.
 - Add `Maybe.equals` and respective `==` operator when the inner type is equatable.
 - Add `inherit_stdio` option to `SubProcessOptions` to inherit parent's stdin, stdout, and stderr instead of creating pipes. #2138
+- Remove superfluous `cleanup` parameter in `os::exit` and `os::fastexit`.
 
 ## 0.7.1 Change list