Improvement: Removed main function from GCD class . Corrected and improved docstring.

[Tanmay-Singh3004]

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized it.
• [x] All filenames are in PascalCase.
• [x] All functions and variable names follow Java naming conventions.
• [x] All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• [x] All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 66.97%. Comparing base (ef72b1e) to head (da2feb4).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5828      +/-   ##
============================================
- Coverage     66.97%   66.97%   -0.01%     
+ Complexity     4522     4520       -2     
============================================
  Files           613      613              
  Lines         16989    16985       -4     
  Branches       3281     3281              
============================================
- Hits          11378    11375       -3     
+ Misses         5163     5160       -3     
- Partials        448      450       +2     

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