Since before the Makefile was introduced, we have removed the go-spew
and go-difflib dependencies, since they are not necessary in order to
build or develop Git LFS.
Homebrew running Go 1.11.1 during build, however, requires them. In the
interim before this commit is released, we run `make vendor RM=true` to
refresh the vendor tree without removing these dependencies. In the
future, we'll be able to remove this changed introduced into Homebrew by
not removing the dependencies in the first place.
Since this commit removes the only usage of $(RM), we remove its
definition, too.
We have historically removed the github.com/davecgh/go-spew library,
because we do not depend on it and therefore would not like to carry its
code.
The 'make vendor' recipe contains a couple of $(RM) invocations to
perform that removal, but it appears that some go-spew code has crept
in via 902e855f (go.mod: update gitobj to the latest master,
2018-08-31).
Before updating the latest changes from gitobj, let's run 'make vendor'
to remove this code, so that our subsequent change is cleaner.
In a future commit, we'll use the latest gitobj's untyped Object
function and storage functionality. Update the repository to the latest
master and vendor the dependencies.
