There's no need to remove semicolon, "b" is the last element of block, semicolon can stay there.
...
And the article is from 1981.
As you said... the article is from 1981.
And in 1981 it was probably
not permitted to leave the semicolon after b because it precedes end. (I just
answered a similar question a few days ago)
In early versions of Pascal it was
not permitted to do a semicolon before end.
The presence of an extra semicolon was not permitted in early versions of Pascal.
(
source)
(I take it, we can assume 33 years ago is "earlier"

)
But you're right... it was a stupid example. The author just didn't realize that the semicolons are for
separating statements
between the begin and end. So a semicolon before end is not needed (and in earlier version not permitted). When understanding that, it makes perfect sense.
Pascal programs start with the program keyword with a list of external file descriptors as parameters[14] (not required in Turbo Pascal etc.); then follows the main block bracketed by the begin and end keywords. Semicolons separate statements, and the full stop (i.e., a period) ends the whole program (or unit). Letter case is ignored in Pascal source.
But nowadays:
Programmers usually include these extra semicolons out of habit, and to avoid changing the last line of a statement sequence when new code is appended.
Yeah... that article is really old.