infra: Remove deprecated documentation

The rd-infra documentation has been moved in april and
a stub now details where it can be found. Remove teh
actual documentation and leave a comment with where
the history can be found in version control.

Signed-off-by: Tom Pilar <tom.pilar@arm.com>
Change-Id: Ibad70bef2b66dd75a4c82acd95b70e4bd600fe75