enlightenment: do not propagate the systemd socket to E17.

In a proper systemd user session setup, enlightenment_start will be
gone. That is still not doable today and as I plan to roll more feature
in EFL regarding systemd, we need to prevent enlightenment to believe
it is the process started by systemd.

src/bin/e_start_main.c

@@ -254,6 +254,8 @@ main(int argc, char **argv)
    Eina_Bool restart = EINA_TRUE;
 #endif
 
+   unsetenv("NOTIFY_SOCKET");
+
    /* Setup USR1 to detach from the child process and let it get gdb by advanced users */
    action.sa_sigaction = _sigusr1;
    action.sa_flags = SA_RESETHAND;