Remove dead links in amp-access-analytics doc (#19588)
Remove dead links in amp-access-analytics doc (#19588)

* Remove dead links in amp-access-analytics doc

Remove links to ./amp-access-spec.md#login-page.  The related content has not yet been added to the Detailed Discussion section of amp-access.md.

* Fix link to amp-var-substitutions doc

Add missing double-dot notation to relative link.  The link was failing a Travis CI test.

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