remove redundant translation cache clearing from TranslationController

[solverat]

Remove redundant Translation::clearDependentCache() calls from TranslationController

• Remove premature cache clear in translationsAction() before save()
  (save() already calls clearDependentCache() internally)
• Remove unnecessary cache clear in exportAction()
  (export does not modify data, no cache invalidation needed)

[solverat]

Background: I had a painfull day of debugging zombie keys within a project with enabled Redis caching.

With Redis, writing a cache entry requires two separate operations: SETEX (write value) and SADD (register in tag set).

These are not atomic. If a second cache invalidation fires between these two operations, the tag registration is lost while the cache entry survives - a "zombie key" that can never be cleared by tag-based invalidation.

Removing the redundant clearDependentCache() call reduces the invalidation waves from two to one, which shrinks the window for this race condition to occur.

And as a final note: Whether this fully resolves the zombie key problem requires further observation in production.