Remove i18n cleanup ({} and extra #) from the i18n scripts

[obulat]

Description

On https://translate.wordpress.org, the {} placeholders in the translation strings are replaced with ### ### placeholders. Then, we replace them back when converting to locale usable by Nuxt app.

However, some placeholders were changed to use an irregular number of #, or to have empty placeholders. We have a hot-fix in the code to replace the extra # or empty {} pairs. We also log that the invalid values were found, and link to this issue in the hot-fix.

When all of the incorrect placeholders are replaced on https://translate.wordpress.org, we can close this issue.

Additional context

Similar issue for kebab-cased keys: #2438