incident_section_gen: fix a memory leak warning.

This fixes the warning
frameworks/base/tools/incident_section_gen/main.cpp:170:48:
warning: Potential memory leak [clang-analyzer-cplusplus.NewDeleteLeaks]

Bug:None
Test: The warning is gone.
Change-Id: I48dbd51ff53b35aa3fcd0b6507485ec61c1a160c