x11-toolkits/p5-Tk: Do not set CONFIGURE_ARGS twice

The port currently sets CONFIGURE_ARGS twice.

The second CONFIGURE_ARGS= overwrites the first, therefore X11INC and
X11LIB are not in CONFIGURE_ARGS. The ports builds anyway, so
the first CONFIGURE_ARGS can be removed.

PR: 234704
Submitted by: tobik