website: fix wrong use of backslash in hardware.adoc

[vladlen]

Summary

mandoc generates texts from nam pages for hardware.adoc .
It escapes _ and [ symbols with backslash, that is displayed
in the web-page. These backslashes were removed manually.
This patch removes all these cases from the current pages.
New pages will be generated by fixed version of the tool
(fixed in https://reviews.freebsd.org/D56646)