backport `next export` no-op to support Next 9

[jlengstorf]

in v1.1.1 of this plugin (still used for next@<=10.0.6), an error is thrown if the site uses next export

in the current plugin, the plugin no-ops instead — this is the desired behavior, because we want to encourage using next export as the preferable way to build sites with Next (it keeps all the benefits of the Jamstack without workarounds)

we need to backport the next export no-op into the v1 codebase and release a v1.1.2 that still supports next@<=10.0.6, but doesn't cause errors if it's installed when using our desired dev approach