[web] stop looking at a request's Cache-Control header
As per RFC 7234 (HTTP 1.1 Caching):
The "Cache-Control" header field is used to specify directives for
caches along the request/response chain.
CubicWeb is not a cache.
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# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
#
# This file is part of CubicWeb.
#
# CubicWeb is free software: you can redistribute it and/or modify it under the
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# any later version.
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# FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
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