COG_SYM_REF_ in cog.md

[redacted34874]

As said in #4,

The COG_SYM_REF_ prefix should probably be stripped off from symbol types since that's engine's internal representation

we shall discuss, where to relocate the relevant documentation entries.

[smlu]

My suggestion would be to remove any engine-related prefixes from names, such as COG_SYM_REF_. Alternatively, it's an option to create separate documentation for engine-specific stuff. However, I think it would have little value to anyone since there is no publicly available engine source code.