Alias sys_mkdir and sys_mkdirat to sys_chmod and sys_fchmodat

Special parsers for mkdir and mkdirat are redundant because
sys_chmod and sys_fchmodat implement the same decoding.

* file.c (decode_mkdir, sys_mkdir, sys_mkdirat): Remove.
* linux/dummy.h (sys_mkdir): Alias to sys_chmod.
(sys_mkdirat): Alias to sys_fchmodat.
* linux/syscall.h (sys_mkdir, sys_mkdirat): Remove.
* pathtrace.c (pathtrace_match): Do not check for sys_mkdirat.
diff --git a/linux/dummy.h b/linux/dummy.h
index 31be7b7..7a8b17c 100644
--- a/linux/dummy.h
+++ b/linux/dummy.h
@@ -68,6 +68,8 @@
 #define	sys_getresgid		sys_getresuid
 #define	sys_lstat		sys_stat
 #define	sys_lstat64		sys_stat64
+#define	sys_mkdir		sys_chmod
+#define	sys_mkdirat		sys_fchmodat
 #define	sys_mlock		sys_munmap
 #define	sys_mq_unlink		sys_chdir
 #define	sys_munlock		sys_munmap