Fix uninstall command

This reverts commit 4904fcf51f.

The `script` variable you were referring to previously is actually the
relative path to a script, for example `bin/mw`.

This fails to remove the script, because, obviously, the path is
incorrect.

I'd suggest renaming `script` to `scriptPath` in line 13
and `shared` to `sharedPath` in line 18
(or whatever variable names you prefer that make it clearer)
to avoid confusion in the future.

Signed-off-by: Kipras Melnikovas <kipras@kipras.org>

for loop directory wildcard includes the directory name. No need to
specify the dir name when removing file.

Signed-off-by: Ayman Bagabas <ayman.bagabas@gmail.com>

This patch puts the environment variable PREFIX in more use. If
specified, mull-wizard Makefile substitute all instances of prefix with
the provided environment variable.

Signed-off-by: Ayman Bagabas <ayman.bagabas@gmail.com>

I was wondering why the install failed... 😆

This would enable users to install to other locations (important e.g. for chroot installs or packaging).