tests.py: Prevent a false positive parse-options memory leak report
tests.py: Prevent a false positive parse-options memory leak report

A reference to the default argument of parse_sent() survives the class
definition and hence its memory remains allocated at script exit, which
leads to a bogus report on a memory leak.

Fix it by deleting parse_sent() when the tests of its class are done.

ampli/link-grammar,linas/link-grammar,ampli/link-grammar,opencog/link-grammar,ampli/link-grammar,ampli/link-grammar,opencog/link-grammar,opencog/link-grammar,linas/link-grammar,opencog/link-grammar,linas/link-grammar,linas/link-grammar,opencog/link-grammar,opencog/link-grammar,opencog/link-grammar,opencog/link-grammar,ampli/link-grammar,ampli/link-grammar,linas/link-grammar,linas/link-grammar,ampli/link-grammar,ampli/link-grammar,opencog/link-grammar,linas/link-grammar,linas/link-grammar,linas/link-grammar,ampli/link-grammar