Remove cite submodule.

[bdice]

Description

This PR is my suggestion for resolving #592 (I chose to remove it -- but we could update that submodule instead, if desired).

Deprecation of the submodule in 1.x is still needed to fully resolve #592.

Motivation and Context

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.

[codecov]

Codecov Report

Merging #594 (981d99d) into next (257c931) will increase coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             next     #594      +/-   ##
==========================================
+ Coverage   83.77%   83.91%   +0.13%     
==========================================
  Files          54       53       -1     
  Lines        5535     5519      -16     
  Branches     1021     1017       -4     
==========================================
- Hits         4637     4631       -6     
+ Misses        668      658      -10     
  Partials      230      230              

Impacted Files	Coverage Δ
signac/__init__.py	100.00% <100.00%> (ø)

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