STYLE: Fix linting of benchmarks
- [x] closes #22884 
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Fixed the following:

` asv_bench/benchmarks/algorithms.py:12:5: E722 do not use bare except'
asv_bench/benchmarks/timeseries.py:1:1: F401 'warnings' imported but unused
asv_bench/benchmarks/stat_ops.py:21:9: E722 do not use bare except'
asv_bench/benchmarks/stat_ops.py:59:9: E722 do not use bare except'
asv_bench/benchmarks/pandas_vb_common.py:5:1: F401 'pandas.Panel' imported but unused
asv_bench/benchmarks/pandas_vb_common.py:12:5: E722 do not use bare except'
asv_bench/benchmarks/pandas_vb_common.py:37:9: E722 do not use bare except'
asv_bench/benchmarks/join_merge.py:32:9: E722 do not use bare except'
asv_bench/benchmarks/io/csv.py:2:1: F401 'timeit' imported but unused
asv_bench/benchmarks/io/csv.py:8:1: F401 'pandas.compat.PY2' imported but unused
asv_bench/benchmarks/io/csv.py:184:80: E501 line too long (87 > 79 characters)  `