remove unnecessary utf-8 header in .py files

[samuelorji]

Description

Remove Unnecessary # -*- coding: utf-8 -*- headers from .py files

Issues Resolved

https://github.com/opensearch-project/opensearch-py/issues/613

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[codecov[bot]]

Codecov Report

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

Comparison is base (5b28423) 71.98% compared to head (b2b8c3e) 71.98%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #615 +/- ## ======================================= Coverage 71.98% 71.98% ======================================= Files 89 89 Lines 7935 7935 ======================================= Hits 5712 5712 Misses 2223 2223 ```

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