testcases: let i3test.pm export $x, adapt testcases

testcases/t/148-regress-floatingmovews.t

@@ -4,15 +4,8 @@
 # Regression test for correct focus behaviour when moving a floating con to
 # another workspace.
 #
-use X11::XCB qw(:all);
 use i3test;
 
-BEGIN {
-    use_ok('X11::XCB::Window');
-}
-
-my $x = X11::XCB::Connection->new;
-
 my $tmp = fresh_workspace;
 
 # open a tiling window on the first workspace