Most of the page_header blocks were removed by previous patches, but
then brought back by regressions in Volumes and Data Processing. This
patch removes those leftover page_header blocks, and removes a few
templates that are not used in Horizon that were found during the
process.
Change-Id: Icbd03f0809a5c664b9b83f06bc398139c3de1184
Closes-Bug: 1436311