Remove test files from the npm package

[Havunen]

F-Secure WithSecure security scanner does not like the test file and is reporting false positive about it.
Never the less, including the test file is waste of network traffic.

https://github.com/koajs/body-parsers/blob/master/test/test.js

[Havunen]

The dependency chain seems to be following:

"koa-better-body": "^3.3.9",

Loads "koa-body-parsers": "tunnckocore/body-parsers#patch-1"

which seems to be hosted here:

https://github.com/tunnckoCore/body-parsers/tree/patch-1

and it contains a test file shipped in the npm package.

[tunnckoCore]

Never the less, including the test file is waste of network traffic.

Valid.