coin-api dependencies

[ivcosla]

btcd is listed as a dependency for dep in this file:
https://github.com/skycoin/services/blob/master/coin-api/Gopkg.toml#L32

However when performing dep ensure I get the following error:

Warning: the following project(s) have [[constraint]] stanzas in Gopkg.toml:

  ✗  github.com/btcsuite/btcd

However, these projects are not direct dependencies of the current project:
they are not imported in any .go files, nor are they in the 'required' list in
Gopkg.toml. Dep only applies [[constraint]] rules to direct dependencies, so
these rules will have no effect.

Either import/require packages from these projects so that they become direct
dependencies, or convert each [[constraint]] to an [[override]] to enforce rules
on these projects, if they happen to be transitive dependencies.

After looking at the go files I realized that btcd is not a dependency to any of the go files. I would like to know if this is actually intended in some way.