ASV: clean/simplify setup methods
Trying to make some of the setup methods a bit more efficient. Might(?) save around a minute total on the ASV job. 

e.g.

```
import time
from itertools import product
from asv_bench.benchmarks.series_methods import NanOps

param_sets = list(product(*NanOps.params))

t = time.time()
for params in param_sets:
    try:
        NanOps().setup(*params)
    except NotImplementedError:
        pass
print(time.time() - t)

# 11.87  -> main
# 1.90   -> PR
```

Thanks @lukemanley 