Merge two warning strings

[pavelevap]

There are a little different strings for warnDelete.

See attached patch.

There is also missing singular string for clicking only on "Delete" link for single item (and not using Bulk edits).

[pavelevap]

BTW, I tested warning strings and there are some other problems:

• For example we have "Storno" button in Internet Explorer, but "Zrušit" in Chrome and Firefox. Is there any chance that these messages could take it into account?

• There is a new line and two spaces in strings, but it looks strange in some browsers. It was probably added due to some historical reasons, I guess...

[SergeyBiryukov]

In 35230:

Merge two warning strings.

Props pavelevap.
Fixes #29740.