Fix documentation issues for 4.x #852

Job	Run time
cs-stan / Coding Standard & Static Analysis	39s
testsuite / testsuite-linux (8.3, highest, false)	38s
testsuite / testsuite-linux (8.2, lowest, false)	33s
testsuite / testsuite-linux (8.2, highest, false)	37s
testsuite / testsuite-linux (8.5, highest, false)	1m 17s
testsuite / testsuite-linux (8.4, highest, false)	1m 18s
	5m 2s

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