chore: taking db dependencies out of requirements-dev.txt

[mistercrunch]

CATEGORY

• Build / Development Environment

SUMMARY

Py deps mysqlclient and psycopg2 really aren't dev dependencies, they're more optional deps, so the right place for them is extra_requires in our setup.py.

Not a big deal, but mysqlclient has os-level deps and that forces people setting up a dev env to jump through unnecessary hoops

[john-bodley]

Any reason to pin these here? Note we may need to have a requirements.in file including the line-e . (and possibly mention of the extra targets) is we want to have a fully pinned environment for testing purposes.

[mistercrunch]

pip-compile doesn't play nicely with extras, there's no way to say give me the descendants on [only] on extra. Related comment in a related PR here: #7372 (comment)

[codecov-io]

Codecov Report

Merging #7605 into master will decrease coverage by 0.04%.
The diff coverage is 40%.

@@            Coverage Diff             @@
##           master    #7605      +/-   ##
==========================================
- Coverage   65.75%   65.71%   -0.05%     
==========================================
  Files         459      459              
  Lines       21980    21980              
  Branches     2415     2415              
==========================================
- Hits        14453    14444       -9     
- Misses       7406     7415       +9     
  Partials      121      121

Impacted Files	Coverage Δ
superset/db_engines/hive.py	0% <0%> (ø)	⬆️
superset/sql_parse.py	99.2% <100%> (ø)	⬆️
superset/db_engine_specs/mysql.py	93.02% <100%> (ø)	⬆️
superset/db_engine_specs/hive.py	39.42% <0%> (-4.33%)	⬇️

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