fix: remove leave policy assignment creation patch

[ruchamahabal]

• This patch was written in feat: Leave policy assignment #23112 where leaves were granted explicitly after creating policy assignments.
• This was refactored in feat: Leave Policy Assignment Refactor #24327 where this redundant "Grant Leaves" button was removed and leaves were granted on submission of policy assignment.
• This patch doesn't seem to be required since policy assignments never used to get created automatically.
• Moreover, creating assignments without Leave Period information, breaks this patch a lot during migrations and there is no other way to patch this.
• If successful, it just allocates leaves arbitrarily on migration based on defaults set in the employee master which is also not correct.

[codecov]

Codecov Report

Merging #31097 (7ae6c90) into develop (5fd31c6) will decrease coverage by 0.29%.
The diff coverage is n/a.

❗ Current head 7ae6c90 differs from pull request most recent head 70a59cd. Consider uploading reports for the commit 70a59cd to get more accurate results

@@             Coverage Diff             @@
##           develop   #31097      +/-   ##
===========================================
- Coverage    63.34%   63.04%   -0.30%     
===========================================
  Files          986      986              
  Lines        67367    67358       -9     
===========================================
- Hits         42673    42468     -205     
- Misses       24694    24890     +196     

Impacted Files	Coverage Δ
...eport/item_variant_details/item_variant_details.py	31.32% <0.00%> (-53.02%)	⬇️
erpnext/hr/doctype/job_opening/job_opening.py	28.20% <0.00%> (-43.59%)	⬇️
...mission/employee_tax_exemption_proof_submission.py	76.92% <0.00%> (-23.08%)	⬇️
...e_sales_analytics/supplier_wise_sales_analytics.py	59.01% <0.00%> (-22.96%)	⬇️
..._declaration/employee_tax_exemption_declaration.py	75.00% <0.00%> (-18.94%)	⬇️
erpnext/regional/india/utils.py	64.50% <0.00%> (-10.92%)	⬇️
...t/accounts/report/sales_register/sales_register.py	70.76% <0.00%> (-7.02%)	⬇️
...urity_shortfall/process_loan_security_shortfall.py	93.75% <0.00%> (-6.25%)	⬇️
erpnext/hr/doctype/job_offer/job_offer.py	82.92% <0.00%> (-4.88%)	⬇️
...e/asset_value_adjustment/asset_value_adjustment.py	86.04% <0.00%> (-3.49%)	⬇️
... and 42 more

[ruchamahabal]

Will look into the failing test test_unmarked_days in a separate PR