Removed slic3r.pl, updated Build.PL with a notice, that the Perl

bindings are optional, not required to run Slic3r.

Build.PL

@@ -1,5 +1,10 @@
 #!/usr/bin/perl
 
+print "This script is currently used for installing Perl dependenices for running\n";
+print "the libslic3r unit / integration tests through Perl prove.\n";
+print "If you don't plan to run the unit / integration tests, you don't need to\n";
+print "install these dependencies to build and run Slic3r.\n";
+
 use strict;
 use warnings;