Remove keystone argument from server-side-graphql-client functions

[timleslie]

We no longer need to support the keystone argument, it should always be used with a context argument.

There's a cursory attempt to update the docs, but these need a complete overhaul/integration into the items API, so not too fussed about having them be completely correct right this minute.

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🦋 Changeset detected

Latest commit: c0e0375

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@keystone-next/server-side-graphql-client-legacy	Major
@keystone-next/benchmarks-legacy	Patch
@keystone-next/example-ecommerce	Patch
@keystone-next/keystone	Patch
@keystone-next/test-utils-legacy	Patch

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