Added poll method in Singly LinkedList

[Abinaya-Murugan]

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 39.86%. Comparing base (7054535) to head (d281dff).

Files	Patch %	Lines
...orithms/datastructures/lists/SinglyLinkedList.java	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5257      +/-   ##
============================================
- Coverage     39.89%   39.86%   -0.03%     
+ Complexity     2450     2449       -1     
============================================
  Files           518      518              
  Lines         15484    15489       +5     
  Branches       2962     2962              
============================================
- Hits           6177     6175       -2     
- Misses         9017     9023       +6     
- Partials        290      291       +1     

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