scroll-view-fade: Remove explicit GLSL version

Cogl sets this for us since commit 2701b93f159bf2d3387cedf2d06fe921ad5641f3.

Setting it twice is illegal and causes compile failures:
error C0204: version directive must be first statement and may not be repeated.

src/st/st-scroll-view-fade.glsl

@@ -17,8 +17,6 @@
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
-#version 120
-
 uniform sampler2D tex;
 uniform float height;
 uniform float width;