go {build,test}: rm -i option
go {build,test}: rm -i option

Looks like it was used to get faster incremental builds.
Nowdays (since Go 1.10) there is no need to use it, because
go build cache is used [1].

This fixes `make binaries` on my system where golang is installed
as read-only snap:

> $ make binaries
> 🐳 bin/swarmd
> go build runtime/cgo: open /snap/go/2635/pkg/linux_amd64/runtime/cgo.a: read-only file system
> direct.mk:100: recipe for target 'bin/swarmd' failed

[1] https://groups.google.com/forum/#!msg/golang-dev/qfa3mHN4ZPA/X2UzjNV1BAAJ

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

dperny/swarmkit-1,docker/swarmkit,docker/swarmkit,dperny/swarmkit-1