fmt: remove unnecessary parentheses after return (fix #11423) (#11435)

vlib/os/file.c.v

@@ -215,7 +215,7 @@ pub fn (mut f File) writeln(s string) ?int {
 	if x < 0 {
 		return error('could not add newline')
 	}
-	return (written + 1)
+	return written + 1
 }
 
 // write_string writes the string `s` into the file

vlib/os/os.c.v

@@ -426,7 +426,7 @@ pub fn is_executable(path string) bool {
 		// 04 Read-only
 		// 06 Read and write
 		p := real_path(path)
-		return (exists(p) && p.ends_with('.exe'))
+		return exists(p) && p.ends_with('.exe')
 	}
 	$if solaris {
 		statbuf := C.stat{}