docs: hide revision and build date from HTML pages

docs: hide revision and build date from HTML pages

Revisions and build dates are stamped in each source rst files and show
up in each HTML pages (Some pages have multiple stamps...). We can see
document version in URL path of artifact and those build info by
clicking 'Show Source' as well.

Let's remove revisions and build dates from HTML pages, but remain in
source files so that developers can identify sources.

Change-Id: Ibd511137ec17c614c9aa624a7190e7ccfc568b7f
Signed-off-by: Ryota MIBU <r-mibu@cq.jp.nec.com>