Don't pass height to RPC calls

[alexanderbez]

When passed nil, Tendermint will assume latest height. Not only does this provide cleaner code, but also fixes a bug where there could be a discrepancy between the consensus height and the node status' height.

/cc @faboweb

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• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry: clog add [section] [stanza] [message]

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[codecov]

Codecov Report

Merging #4307 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4307   +/-   ##
=======================================
  Coverage   59.38%   59.38%           
=======================================
  Files         214      214           
  Lines       14531    14531           
=======================================
  Hits         8629     8629           
  Misses       5264     5264           
  Partials      638      638

[alessio]

Looks good! ACK'd - pending changelog entry