Some minor cleanup

[wezrule]

Removed representation_add () in ledger.cpp. It has an unused nano::transaction parameter and calling the contents of the function (1 line) directly where it's used seems cleaner than the extra indirection of this function.

Removed multi-line commented section of code in core_test/epochs.cpp. It references an epoch_2 which doesn't currently exist, so will just confuse anyone looking at it.

nano/secure/CMakeLists.txt to be consistent with the rest of the file the header goes before the source file.

The confirmation height processor now has a dependency on the ledger class and the constructor is passed a cemented_count cache from the ledger, this can just be called from the ledger object directly now, no need to pass it in.

Some functions in ledger/epoch can return const & to avoid a copy.

Using auto to simplify some lambda parameters in epoch.cpp and pass the link capture by reference