Remove database and host components.

[bdice]

Description

This PR follows #575.

• Remove database and host components.
• Update docs/setup files.

Motivation and Context

Part of signac 2.0 API cleanup.

Types of Changes

• Documentation update
• Bug fix
• New feature
• Breaking change¹

¹The change breaks (or has the potential to break) existing functionality.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• My code follows the code style guideline of this project.
• The changes introduced by this pull request are covered by existing or newly introduced tests.

If necessary:

• I have updated the API documentation as part of the package doc-strings.
• I have created a separate pull request to update the framework documentation on signac-docs and linked it here.
• I have updated the changelog and added all related issue and pull request numbers for future reference (if applicable). See example below.

[mikemhenry]

tasty
+13 −1,067

[codecov]

Codecov Report

Merging #576 (8c25029) into next (e8e949f) will increase coverage by 1.93%.
The diff coverage is 57.14%.

@@            Coverage Diff             @@
##             next     #576      +/-   ##
==========================================
+ Coverage   80.48%   82.42%   +1.93%     
==========================================
  Files          59       54       -5     
  Lines        6319     5850     -469     
  Branches     1179     1097      -82     
==========================================
- Hits         5086     4822     -264     
+ Misses        945      785     -160     
+ Partials      288      243      -45     

Impacted Files	Coverage Δ
signac/contrib/utility.py	47.79% <ø> (-4.06%)	⬇️
signac/core/utility.py	91.30% <ø> (+19.08%)	⬆️
signac/__main__.py	74.72% <50.00%> (+3.32%)	⬆️
signac/__init__.py	100.00% <100.00%> (ø)
signac/common/validate.py	39.13% <0.00%> (-34.79%)	⬇️
signac/common/config.py	67.28% <0.00%> (-14.02%)	⬇️

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[bdice]

@vyasr @tommy-waltmann I assigned you as reviewers because Brandon (the suggested committer) is out this week and you two were some of the last developers to touch these files. This PR is a dependency of #580, which I will re-work once this PR is merged.