Fix client-admin SignOut story

[patcon]

Getting an error for this:

http://civictechto.github.io/polis-storybook?path=/story/compdem-client-admin-signout--default

TypeError: Failed to construct 'URL': Invalid URL
    at Function.ajax (http://localhost:6006/main.iframe.bundle.js:322:32)
    at signoutPost (http://localhost:6006/_storybook_decorators_js.iframe.bundle.js:914:58)
    at http://localhost:6006/_storybook_decorators_js.iframe.bundle.js:924:16
    at Object.dispatch (http://localhost:6006/vendors-node_modules_theme-ui_theme-provider_dist_index_esm_js-node_modules_react-redux_es_in-8925c8.iframe.bundle.js:5486:18)
    at SignOut.componentDidMount (http://localhost:6006/compdem-client-admin-SignOut-stories.iframe.bundle.js:306:20)
    at commitLifeCycles (http://localhost:6006/vendors-node_modules_storybook_addon-a11y_dist_preview_mjs-node_modules_storybook_addon-essen-e6ba31.iframe.bundle.js:64765:22)
    at commitLayoutEffects (http://localhost:6006/vendors-node_modules_storybook_addon-a11y_dist_preview_mjs-node_modules_storybook_addon-essen-e6ba31.iframe.bundle.js:67754:7)
    at HTMLUnknownElement.callCallback (http://localhost:6006/vendors-node_modules_storybook_addon-a11y_dist_preview_mjs-node_modules_storybook_addon-essen-e6ba31.iframe.bundle.js:45139:14)
    at Object.invokeGuardedCallbackDev (http://localhost:6006/vendors-node_modules_storybook_addon-a11y_dist_preview_mjs-node_modules_storybook_addon-essen-e6ba31.iframe.bundle.js:45188:16)
    at invokeGuardedCallback (http://localhost:6006/vendors-node_modules_storybook_addon-a11y_dist_preview_mjs-node_modules_storybook_addon-essen-e6ba31.iframe.bundle.js:45243:31)

Seems to be related to this:

polis-storybook/.storybook/preview.js

Line 27 in 6216fcb

const mockedPathname = new URL(params.url).pathname

but can't make it go away by adding a new entry to this for /api/v3/auth/deregister to this:

polis-storybook/.storybook/preview.js

Lines 34 to 39 in 6216fcb

	global.$.ajax = ajax_responses({
	'/api/v3/math/pca2': getMath(),
	'/api/v3/comments': [getComments()],
	'/api/v3/votes': [],
	'/api/v3/votes/famous': getVotesFamous(),
	})

related to this action being run in <SignOut />

https://github.com/CivicTechTO/polis/blob/24604e5fa1a1e32357b18237b33510c26d3bd3fb/client-admin/src/actions/index.js#L612-L620

Needs troubleshooting