Improve scheduled reminder form labels. Resolves issue core/3823

[artfulrobot]

Overview

See https://lab.civicrm.org/dev/core/-/issues/3823

Before

Inaccurate confusing labels re effective start/end dates.

After

Simpler and more accurate labels.

Technical Details

The changes are to texts, but also removing the clever javascript code that was needed to write the previous nonsensical labels 😆

[civibot]

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[demeritcowboy]

My head hurts now. Did a quick test and I've confirmed for the 10th time now I don't really understand scheduled reminders. But I think this seems to match my test.

Getting rid of the unnecessary javascript is worth merging.

[artfulrobot]

Thanks @demeritcowboy !