Shaders: drop useless const from function declarations.

src/Magnum/Shaders/FlatGL.h

@@ -1064,7 +1064,7 @@ template<UnsignedInt dimensions> class MAGNUM_SHADERS_EXPORT FlatGL: public GL::
          * @requires_webgl20 Skinning requires integer support in shaders,
          *      which is not available in WebGL 1.0.
          */
-        FlatGL<dimensions>& setJointMatrices(const Containers::ArrayView<const MatrixTypeFor<dimensions, Float>> matrices);
+        FlatGL<dimensions>& setJointMatrices(Containers::ArrayView<const MatrixTypeFor<dimensions, Float>> matrices);
 
         /**
          * @overload

src/Magnum/Shaders/MeshVisualizerGL.h

@@ -947,7 +947,7 @@ class MAGNUM_SHADERS_EXPORT MeshVisualizerGL2D: public Implementation::MeshVisua
          * @requires_webgl20 Skinning requires integer support in shaders,
          *      which is not available in WebGL 1.0.
          */
-        MeshVisualizerGL2D& setJointMatrices(const Containers::ArrayView<const Matrix3> matrices);
+        MeshVisualizerGL2D& setJointMatrices(Containers::ArrayView<const Matrix3> matrices);
 
         /**
          * @overload

src/Magnum/Shaders/PhongGL.h

@@ -1672,7 +1672,7 @@ class MAGNUM_SHADERS_EXPORT PhongGL: public GL::AbstractShaderProgram {
          * @requires_webgl20 Skinning requires integer support in shaders,
          *      which is not available in WebGL 1.0.
          */
-        PhongGL& setJointMatrices(const Containers::ArrayView<const Matrix4> matrices);
+        PhongGL& setJointMatrices(Containers::ArrayView<const Matrix4> matrices);
 
         /**
          * @overload