chore(*): Remove deprecated date formats.

[MayaKirova]

Closes #16139

These were set but were never used when resolving the date formats in excel, so no point in keeping them.

Additional information (check all that apply):

• Bug fix
• New functionality
• Documentation
• Demos
• CI/CD

Checklist:

• All relevant tags have been applied to this PR
• This PR includes unit tests covering all the new code (test guidelines)
• This PR includes API docs for newly added methods/properties (api docs guidelines)
• This PR includes feature/README.MD updates for the feature docs
• This PR includes general feature table updates in the root README.MD
• This PR includes CHANGELOG.MD updates for newly added functionality
• This PR contains breaking changes
• This PR includes ng update migrations for the breaking changes (migrations guidelines)
• This PR includes behavioral changes and the feature specification has been updated with them

[Copilot]

Pull request overview

This PR removes unused, deprecated Angular locale date format utilities from the grid export pipeline, aligning the exporter code with the current locale/formatting implementation and addressing issue #16139’s note about deprecated APIs not affecting the Excel export output.

Changes:

• Removed the deprecated getLocaleDateFormat / getLocaleDateTimeFormat usage from the exporter column-mapping logic.
• Dropped the now-unneeded @angular/common import (FormatWidth, getLocaleDateFormat, getLocaleDateTimeFormat) from the base export service.