TextureCache: Ensure that all render target textures have as many layers as the frame buffer.

Also fixes a case where the D3D code path did not initialize num_layers leading to undefined behaviour.

Source/Core/VideoBackends/OGL/FramebufferManager.cpp

@@ -21,8 +21,6 @@ int FramebufferManager::m_targetHeight;
 int FramebufferManager::m_msaaSamples;
 
 GLenum FramebufferManager::m_textureType;
-int FramebufferManager::m_EFBLayers;
-
 GLuint FramebufferManager::m_efbFramebuffer;
 GLuint FramebufferManager::m_xfbFramebuffer;
 GLuint FramebufferManager::m_efbColor;