Fix SSAO render pass

Fixes 3 issues in the SSAO shader:

1. Use texture formats (RGBA16F) required to be color-renderable in the OpenGL specification (see Req. Rend. column in the table below) instead of RGB16F
2. Remove depth texture after RenderDelegate because it is read in the RenderSSAO pass, which can cause problems in some OpenGL implementations
3. Fix implicit conversions from ivec2 to vec2 in the GLSL code