Follows similar commits to the objectcache, rdbms, profiler,
filerepo components and other areas [1].
* Remove duplicate descriptions from file blocks in favour of class
doc blocks. This reduces needless duplication and was often
incorrect or outdated, and helps (ironically) to make the file header
more consistently visually ignorable.
* Remove `ingroup` from file blocks in class files as otherwise
the file is indexed twice (e.g. in Doxygen) which makes navigation
more messy.
* Remove use of AtEase.
[1] https://gerrit.wikimedia.org/r/q/message:ingroup+owner:Krinkle
Change-Id: Ic31c1a3e7ac66b8cdc528f4382104181841ccd12
