Remove (now) unused decodeNormF GLSL shader.

indra/newview/app_settings/shaders/class1/environment/decodeNormF.glsl

-/**
- * @file decodeNormF.glsl
- *
- * $LicenseInfo:firstyear=2018&license=viewerlgpl$
- * Second Life Viewer Source Code
- * Copyright (C) 2018, Linden Research, Inc.
- * 
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation;
- * version 2.1 of the License only.
- * 
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- * 
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
- * 
- * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
- * $/LicenseInfo$
- */
-
-vec3 decode_normal (vec2 enc)
-{
-    vec2 fenc = enc*4-2;
-    float f = dot(fenc,fenc);
-    float g = sqrt(1-f/4);
-    vec3 n;
-    n.xy = fenc*g;
-    n.z = 1-f/2;
-    return n;
-}
-