Resolve "delete called on non-final" warnings.

[donpellegrino]

Two warnings are issued by the Intel compiler on the codebase for "delete called on non-final":

src/static/suffixtree/LCP_PT.cpp:236:3: warning: delete called on non-final 'cds_static::RMQ_succinct' that has virtual functions but non-virtual destructor [-Wdelete-non-abstract-non-virtual-dtor]
                delete (RMQ_succinct *)rmq;
                ^
src/static/suffixtree/SuffixTreeY.cpp:464:3: warning: delete called on non-final 'cds_static::TextIndexCSA' that has virtual functions but non-virtual destructor [-Wdelete-non-abstract-non-virtual-dtor]
                delete (TextIndexCSA *)csa;
                ^