remove calls to DataFrame.consolidate in benchmarks
The ``DataFrame.consolidate`` method has been removed for 0.24 (in #23377), but there are still some calls to it in the asv benchmarks.  I had a failure in #23752 because of this, so hereby a fix.

This PR uses the internal  ``_consolidate`` method instead.
Hello @topper-123! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`asv_bench/benchmarks/frame_methods.py`](https://github.com/topper-123/pandas/blob/78650a9ffc9cd43d11d123db19c575e6ccbcf4ba/asv_bench/benchmarks/frame_methods.py) !

 - There are no PEP8 issues in the file [`asv_bench/benchmarks/join_merge.py`](https://github.com/topper-123/pandas/blob/78650a9ffc9cd43d11d123db19c575e6ccbcf4ba/asv_bench/benchmarks/join_merge.py) !

 thanks @topper-123 