Remove unused variable

[Shweta-281]

Description

This PR addresses a static analysis warning in the monumentCheckIn method where a local variable doc was declared but never used. By removing the unused variable, we improve code quality, reduce technical debt, and ensure adherence to Dart best practices. This fix aligns with GSOC goals of fostering clean, maintainable, and efficient codebases.

Changes:
File: lib/data/repositories/firebase_social_repository.dart

Method: monumentCheckIn

Issue: Unused doc variable when creating a check-in post.

Fix: Remove the assignment of the unused DocumentReference variable.

Before:

dart
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DocumentReference doc = await _database.collection("posts").add({ ... });
After:

dart
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await _database.collection("posts").add({ ... });
Impact:
✅ Eliminates static analysis warnings.

✅ Reduces clutter and improves code readability.

✅ Demonstrates attention to code quality, a key GSOC evaluation criterion.

Fixes # 344

Please delete options that are not relevant.

• 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 not work as expected)
• Refactor (does not change functionality, e.g. code style improvements, linting)
• Documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

Please include screenshots below if applicable.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

Maintainer Checklist

• closes Unused Local Variable Warning in monumentCheckIn Method #344(Replace xxxx with the GitHub issue number)
• Tag the PR with the appropriate labels