Fix PERFORM VARYING AFTER example

[tanto259]

Signed-off-by: Hartanto Ario Widjaya 13640520+tanto259@users.noreply.github.com

Proposed changes

This PR edit the example of the PERFORM VARYING AFTER example to reflect that it only accepts out-of-line statement contained within a paragraph.

From the Language Reference, phrase 2 is only available via PERFORM procedure-statement-1:

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