Linting fixes of dynamicsampler.py

[segasai]

Some pylint driven style improvements (remove unused variables, etc)

[coveralls]

Pull Request Test Coverage Report for Build 872841099

• 76 of 103 (73.79%) changed or added relevant lines in 6 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.02%) to 71.906%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
py/dynesty/dynamicsampler.py	7	10	70.0%
py/dynesty/sampler.py	6	11	54.55%
py/dynesty/plotting.py	53	72	73.61%
<!--	Total:	76	103	73.79%	-->

Totals
Change from base Build 872557383:	-0.02%
Covered Lines:	3381
Relevant Lines:	4702

---

💛 - Coveralls

[segasai]

This should be ready to review/merge after the tests on the last commit are done, The main change here is that now pylint is being run in a more strict mode (that would have caught a previous oversight with saved_* stuff). That also forced me to change the constructors of the samplers ensuring that the super() call is happening at the beginning to avoid overriding. Since the branch was started before the recent merge, I've had to cherry-pick a couple of commits here. The conflicts should be resolved in favour of the nestedsamplers.py from this branch.