linker: Don't dynamically allocate slots for linked shaders

The can be at most one shader per stage.  There are currently only two
stages.  There is zero reason to dynamically size this array.

src/glsl/linker.cpp

@@ -823,8 +823,6 @@ link_shaders(struct gl_shader_program *prog)
       goto done;
 
 
-   prog->_LinkedShaders = (struct gl_shader **)
-      calloc(2, sizeof(struct gl_shader *));
    prog->_NumLinkedShaders = 0;
 
    if (num_vert_shaders > 0) {