twister: coverage: Remove dead code at BinaryHandler

BinaryHandler.hanlde() method was trying to call GCOV and fails
silently because of incorrect call parameters. Moreover, even
being fixed, this call is not needed here as it attempts to
find and process .gcno and .gcna files (using wrong paths)
to create .gcov coverage text reports.
Currently the CoverageTool class does all data processing
and report generation using GCOVR or LCOV tools instead of
direct calls to GCOV.

Signed-off-by: Dmitrii Golovanov <dmitrii.golovanov@intel.com>