Fix the last update to the Czech Translation

[milanmajchrak]

References

#4219

Description

The Czech translation was updated by michdyk here: https://github.com/DSpace/dspace-angular/pull/4219/files#diff-2adb7da35ea504568231fb86fa719a689e0df38dc0205425cddc23a1ef47f2e7, but the changes are not accurate or consistent across all thumbnail-related translations. We suggest reverting the last update, as the previous translation was more accurate and consistent.

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[tdonohue]

👍 Thanks @milanmajchrak for your feedback. Since this is simply reverting changes, I'll merge this immediately