Summary:
~DBWithTTLImpl() fails after calling Close() function (will invoke the
Close() function of DBImpl), because the Close() function deletes
default_cf_handle_ which is used in the GetOptions() function called
in ~DBWithTTLImpl(), hence lead to segfault.

Fix by creating a Close() function for the DBWithTTLImpl class and do
the close and the work originally in ~DBWithTTLImpl(). If the Close()
function is not called, it will be called in the ~DBWithTTLImpl()
function.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5485

Test Plan: make clean;  USE_CLANG=1 make all check -j

Differential Revision: D15924498

fbshipit-source-id: 567397fb972961059083a1ae0f9f99ff74872b78