Bug 9819 - 'stopwords'-related code removed

Bug 9819 - 'stopwords'-related code removed

This patch removes code related to stopwords usage. The following methods are removed:

C4::Search->remove_stopwords
C4::Context->stopwords
C4::Context->_new_stopwords

And the buildQuery API was changed (removed the \@removed_stopwords return value).
A follow-up is provided for database changes, to make rebasing easier.

To test:
- Apply this patch
- Do some searches in both intranet and opac interfaces
- Nothing should break

Sponsored-by: Universidad Nacional de Córdoba
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>