Bug 10952: (follow-up) comments fixes and unit tests

Bug 10952: (follow-up) comments fixes and unit tests

- Remove unit tests for ParseSearchHistoryCookie, which doesn't exist
  anymore
- Add unit tests for ParseSearchHistorySession and
  SetSearchHistorySession
- Remove/Modify comments about search history cookie

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Tests fixed and moved, and comments tidied up

Signed-off-by: Charlene Criton <charlene.criton@univ-lyon2.fr>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit bbf7cd6876e94865492e3fd19e59c31b6b95b588)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>