remove WNP dead code

[wen-2018]

If this changeset needs to go into the FXC codebase, please add the WMO and FXC label.

One-line summary

This PR removes WNP 146 donate related dead code.

Significant changes and points to review

Issue / Bugzilla link

https://mozilla-hub.atlassian.net/browse/WT-1380
#17241 (comment)

Testing

• verify nothing is referencing deleted code

[Copilot]

Pull request overview

This PR removes the Firefox “What’s New” v146 donation experience (template, styling, localization, and routing) from Bedrock, cleaning up WNP 146 donate-related dead code.

Changes:

• Removes the firefox_whatsnew_146_donate static bundle and deletes its SCSS source.
• Removes the whatsnew-donate Fluent resource and Pontoon configuration entry.
• Removes the dedicated whatsnew-fx146-donate.html template and the corresponding selection logic in WhatsnewView.

Reviewed changes

Copilot reviewed 6 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
media/static-bundles.json	Drops the firefox_whatsnew_146_donate bundle entry so it’s no longer built/served.
media/css/firefox/whatsnew/whatsnew-146-donate.scss	Removes now-unused styling for the v146 donate variant.
l10n/en/firefox/whatsnew/whatsnew-donate.ftl	Removes the now-unused Fluent strings for the v146 donate variant.
l10n/configs/pontoon.toml	Removes Pontoon path configuration for the deleted whatsnew-donate.ftl resource.
bedrock/firefox/views.py	Removes v146 donate template mapping and routing/selection logic.
bedrock/firefox/templates/firefox/whatsnew/whatsnew-fx146-donate.html	Deletes the v146 donate variant template.

[janriokrause]

r+ 🧹🧼🫧

[janriokrause]

Nice work going beyond my original note. I'd only flagged the ftl_files_map entry, but you also pulled out the version.startswith("146.") branch in get_template_names, the whatsnew-146-donate.scss source, and the pontoon.toml path block. Thanks for thinking past the checklist 😊