Update SuperSU to 2.40

The SuperSU install process is getting rather complicated, so we
will modify the install script slightly and use it to install
all the things and stop trying to check to see if root permissions
have been lost like we used to do.

Change-Id: Ibdb64c909d2bd16e12bb35b4f31f572cc29add47

twrp.cpp

@@ -346,10 +346,6 @@ int main(int argc, char **argv) {
 			if (gui_startPage("installsu") != 0) {
 				LOGERR("Failed to start SuperSU install page.\n");
 			}
-		} else if (TWFunc::Check_su_Perms() > 0) {
-			// su perms are set incorrectly
-			LOGINFO("Root permissions appear to be lost... fixing. (This will always happen on 4.3+ ROMs with SELinux.\n");
-			TWFunc::Fix_su_Perms();
 		}
 		sync();
 		PartitionManager.UnMount_By_Path("/system", false);