Fix IAVL Store Commit

[alexanderbez]

MutableTree#DeleteVersion only returns standard errors now.

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[codecov]

Codecov Report

Merging #4880 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master    #4880   +/-   ##
=======================================
  Coverage   54.05%   54.05%           
=======================================
  Files         269      269           
  Lines       17116    17116           
=======================================
  Hits         9252     9252           
  Misses       7178     7178           
  Partials      686      686

[ethanfrey]

I think it is best to keep the same logic (and add a test).

You rightly noted that this broke as the iavl error format changes:

	if _, ok := tree.versions[version]; !ok {
		return errors.Wrap(ErrVersionDoesNotExist, "")
	}

https://github.com/tendermint/iavl/blob/master/mutable_tree.go#L436-L438

This can be detected (safely) with errors.Cause(err) == iavl.ErrVersionDoesNotExist.

I would propose simply changing the original line:
if err != nil && err.(cmn.Error).Data() != iavl.ErrVersionDoesNotExist {
to
if err != nil && errors.Cause(err) != iavl.ErrVersionDoesNotExist {

That seems the cleaner fix (and maybe a test there)