benchmarks do not compile after removing lease t1 and t2

benchmarks do not compile after removing lease t1 and t2

generic_lease_mgr_benchmark.cc: In member function ‘void isc::dhcp::bench::GenericLeaseMgrBenchmark::prepareLeases6(const size_t&)’:
generic_lease_mgr_benchmark.cc:168:16: error: ‘struct isc::dhcp::Lease6’ has no member named ‘t1_’
         lease->t1_ = i;
                ^~~
generic_lease_mgr_benchmark.cc:169:16: error: ‘struct isc::dhcp::Lease6’ has no member named ‘t2_’
         lease->t2_ = i;
                ^~~
Makefile:677: recipe for target 'run_benchmarks-generic_lease_mgr_benchmark.o' failed