drop transitive dependency on github.com/stretcher/testify for consumers

[bmoffatt]

🤷‍♂️ Did this trigger a warning in a consuming package you have? The dependency only comes in for running this package's unit tests, so it'd interesting & unexpected if the vulnerable dependency was being transitively picked up in the consumer.

bryan@air yolo % cat main.go
package main

import (
	"github.com/aws/aws-lambda-go/lambda"
)

func main() {
	lambda.Start(func() {})
}

bryan@air yolo % cat go.mod
module yolo

go 1.18

require github.com/aws/aws-lambda-go v1.32.0

bryan@air yolo % cat go.sum
github.com/aws/aws-lambda-go v1.32.0 h1:i8MflawW1hoyYp85GMH7LhvAs4cqzL7LOS6fSv8l2KM=
github.com/aws/aws-lambda-go v1.32.0/go.mod h1:IF5Q7wj4VyZyUFnZ54IQqeWtctHQ9tz+KhcbDenr220=
github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/stretchr/testify v1.6.1 h1:hDPOHmpOpP40lSULcqw7IrRb/u7w6RpDC9399XyoNd0=
gopkg.in/yaml.v3 v3.0.0-20200615113413-eeeca48fe776 h1:tQIYjPdBoyREyB9XMu+nnTclpTYkz2zFM+lzLJFO4gQ=

ahh, must be because of the gitHub.com/aws/aws-lambda-go/test package being in the repo

https://github.com/aws/aws-lambda-go/blob/main/events/test/jsoncompare.go#L8

Originally posted by @bmoffatt in #446 (comment)

---

Dropping a go.mod into the folder might be sufficient to break the resolution for consumers, unless of course there's an explicit import of github.com/aws/aws-lambda-go/events/test.

May also consider deleting the package, as it doesn't provide value over direct use of testify in the _test.go files. However... I know I've seen an internal codebase of ours import from this package, so that'd be a breaking change for someone else's unit testing.

[bmoffatt]

After reading about go test all, I believe that removing these entries from a consumer's go.sum file isn't feasible