Makefile: fix parrallel (-j) installs

Currently, we would remove previously installed patches before
installing the new ones. Unfortunately, that does not play well
with heavily parallel installs.

Now, we consider it is the responsibility of the user to first
uninstall any previous version before installing a new one.

Reported-by: Markos Chandras <markos.chandras@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 COPYING