removed fake file system usage, update fs-extra to v11

[shazron]

Closes #631

• Removes usage of the fake filesystem in tests because of incompatibility with fs-extra@11.x (see build(deps): bump fs-extra from 10.1.0 to 11.1.0 #631)

How Has This Been Tested?

• npm test

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #656 (1d7340b) into master (f1088f1) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #656   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           54        54           
  Lines         2832      2832           
  Branches       532       532           
=========================================
  Hits          2832      2832           

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