Reorganize tests with the new "fetch method" suite
Reorganize tests with the new "fetch method" suite

The Headers, Request, and Response suites should mainly be exercising
those classes and not invoking the `fetch` method. Most of those tests
that do have now been moved to the "fetch method" suite.

zebulonj/fetch-plus,benestudio/fetch,JhansiYarnagula/dummy2,github/fetch,benestudio/fetch,JhansiYarnagula/dummy2,zebulonj/fetch-plus,benestudio/fetch,JhansiYarnagula/dummy2,zebulonj/fetch-plus,aleclarson/fetch