refactor(crypto): remove extraneous Client class

[faustbrian]

Proposed changes

Remove the extraneous Client class which serves no real purpose as everything is accessible via imports.

Types of changes

• Refactoring (improve a current implementation without adding a new feature or fixing a bug)

Checklist

• I have read the CONTRIBUTING documentation
• Lint and unit tests pass locally with my changes

[ghost]

The ci/circleci: test-node11-unit job is failing as of 6592973f3f32b3ced7ee7702bcb53e9052888e63. Please review the logs for more information.

Once you've pushed the fixes, the build will automatically re-run. Thanks!

[codecov-io]

Codecov Report

Merging #2417 into 2.4 will decrease coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              2.4    #2417      +/-   ##
==========================================
- Coverage   68.29%   68.24%   -0.06%     
==========================================
  Files         401      400       -1     
  Lines        8615     8600      -15     
  Branches      432      391      -41     
==========================================
- Hits         5884     5869      -15     
- Misses       2686     2687       +1     
+ Partials       45       44       -1

Impacted Files	Coverage Δ
packages/crypto/src/managers/config.ts	98.03% <ø> (ø)	⬆️
packages/crypto/src/identities/keys.ts	100% <100%> (ø)	⬆️
packages/core-tester-cli/src/signer.ts	87.5% <100%> (-0.74%)	⬇️
packages/core-logger-winston/src/formatter.ts	46.15% <0%> (ø)	⬆️

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