Reduce dependencies

[ldemailly]

testify pulls in a lot of stuff and you only use a few asserts equal/true etc for which I have a drop in very light replacement (if you want) https://github.com/fortio/assert

ps: yes it's only for tests yet it impacts go.sum, downloads and ... running tests

[scalalang2]

thanks for the contribution : )
I like this, thx @ldemailly

dependencies of fortio

module fortio.org/assert

go 1.18

dependencies of stretchr/testify

module github.com/stretchr/testify

// This should match the minimum supported version that is tested in
// .github/workflows/main.yml
go 1.17

require (
	github.com/davecgh/go-spew v1.1.1
	github.com/pmezard/go-difflib v1.0.0
	github.com/stretchr/objx v0.5.2
	gopkg.in/yaml.v3 v3.0.1
)

// Break dependency cycle with objx.
// See https://github.com/stretchr/objx/pull/140
exclude github.com/stretchr/testify v1.8.2