chore: remove deprecated print format

[sagarvora]

The format GST POS Invoice exists for two DocTypes: Sales Invoice and POS Invoice.

However, while syncing the one for POS Invoice always overwrites the one for Sales Invoice. Hence, removing files for the Sales Invoice format.

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When searching for a print format called GST POS Invoice, only the one for POS Invoice is visible:

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Alternate solution: keep this format with a different name.

[codecov]

Codecov Report

Merging #29754 (d93d2a8) into develop (77be982) will increase coverage by 6.85%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop   #29754      +/-   ##
===========================================
+ Coverage    52.07%   58.92%   +6.85%     
===========================================
  Files         1111     1112       +1     
  Lines        69408    69547     +139     
===========================================
+ Hits         36146    40984    +4838     
+ Misses       33262    28563    -4699     

Impacted Files	Coverage Δ
...eport/item_variant_details/item_variant_details.py	31.32% <0.00%> (-56.63%)	⬇️
...tch_item_expiry_status/batch_item_expiry_status.py	69.23% <0.00%> (-25.00%)	⬇️
...wise_balance_history/batch_wise_balance_history.py	68.96% <0.00%> (-24.14%)	⬇️
...payroll/doctype/income_tax_slab/income_tax_slab.py	83.33% <0.00%> (-16.67%)	⬇️
...xt/stock/report/stock_analytics/stock_analytics.py	80.19% <0.00%> (-12.88%)	⬇️
...value/warehouse_wise_item_balance_age_and_value.py	92.40% <0.00%> (-2.54%)	⬇️
...saction/incorrect_balance_qty_after_transaction.py	97.67% <0.00%> (-2.33%)	⬇️
...t/product_bundle_balance/product_bundle_balance.py	79.54% <0.00%> (-2.28%)	⬇️
...pnext/accounts/report/gross_profit/gross_profit.py	86.77% <0.00%> (-1.95%)	⬇️
...r/doctype/leave_ledger_entry/leave_ledger_entry.py	90.16% <0.00%> (-1.64%)	⬇️
... and 194 more