[lldb][Posix] Remove unused includes in file system

You could remove unistd.h and it builds, but only because
something else included it. So I've left it in in the spirit
of "include what you use".

Author: DavidSpickett

lldb/source/Host/posix/FileSystemPosix.cpp

@@ -9,12 +9,7 @@
 #include "lldb/Host/FileSystem.h"
 
 // C includes
-#include <dirent.h>
 #include <fcntl.h>
-#include <sys/mount.h>
-#include <sys/param.h>
-#include <sys/stat.h>
-#include <sys/types.h>
 #include <unistd.h>
 #if defined(__NetBSD__)
 #include <sys/statvfs.h>