cubicweb-frbr #3899597 Remove unused indexes [validation pending]

Some indexes on string attributes should be removed.

prioritynormal
typebug
done in0.1.2
load0.100
load left0.000
closed by#b2a1e1b6b1d4 [schema] Fix String indexing attribute on title, closes #3899597
patch[schema] Fix String indexing attribute on title [applied]