checks: flake8 F841 (local variable assigned to but never used) fixes in scripts directory part 1

[mshukuno]

Description

Flake8 F841 (local variable assigned to but never used) fixes in the scripts directory, specifically, d.polar and r.in.wms.

Motivation and context

Changes require resolving a part of Flake8 warnings that are currently ignored. The issue title and number as follows.

• [Bug] Fix currently ignored Flake8 warnings #1522

How has this been tested?

• d.polar: Tested with test_d_polar.py and all passed.

• r.in.wms: Since this tool doesn't have gunittest, I tested with GUI entered parameters following. Test was successful.
  r.in.wms url="https://tiles.maps.eox.at/wms?" layers=s2cloudless output=sentinel2 format=png

Types of changes

Delete unused variables and entire variable declarations.

• 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 before)

Checklist

• PR title provides summary of the changes and starts with one of the
  pre-defined prefixes
• My code follows the code style
  of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.