[#1032] Remove obsolete files:

These appear to have been brought over from LJ for admin purposes but
not used / linked to from anywhere:

* misc/blockedlink
* misc/entry_redirect

From beta period:
* misc/downgrader
[#1032] Convert htdocs/misc/feedping.bml from BML
[#1032] Convert /misc/adult_* from BML

Also converts to Foundation since that was straightforward
[#1032] Convert htdocs/misc/get_domain_session.bml
Merge pull request #1034 from afuna/bml-htdocs-misc-bug-1032

Convert some files in htdocs/misc