gsl.inc: Remove `do_stage`.

gsl.inc: Remove `do_stage`.

Inkscape fails to build after commit c2c8fe [1] with the following error.

    | checking for CAIRO_USER_FONTS... yes
    | checking for INKSCAPE... configure: error: Package requirements (gdkmm-2.4  glibmm-2.4 giomm-2.4 gtkmm-2.4 >= 2.10.0  gtk+-2.0  libxml-2.0 >= 2.6.11  libxslt >= 1.0.15  cairo  sigc++-2.0 >= 2.0.12    gthread-2.0 >= 2.0 libpng >= 1.2 gsl) were not met:
    |
    | No package 'gsl' found
    |
    | Consider adjusting the PKG_CONFIG_PATH environment variable if you
    | installed software in a non-standard prefix.
    |
    | Alternatively, you may set the environment variables INKSCAPE_CFLAGS
    | and INKSCAPE_LIBS to avoid the need to call pkg-config.
    | See the pkg-config man page for more details.
    |
    | ERROR: Function do_configure failed
    NOTE: package inkscape-0.48.0-r0: task do_configure: Failed
    ERROR: TaskFailed event exception, aborting
    ERROR: Build of /home/paul/oe/openembedded/recipes/inkscape/inkscape_0.48.0.bb do_configure failed

Removing `do_stage` fixes building `inkscape_0.48.0.bb` with `angstrom-2008.1`, `angstrom-2010.x` and `minimal` for `MACHINE = "beagleboard"`.

[1] http://cgit.openembedded.org/cgit.cgi/openembedded/commit/?id=c2c8fe4c5629add94bd0b922f5b3446624a9f4d8

Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
Acked-by: Andreas Oberritter <obi@opendreambox.org>