FindJPEG: Revert "Search for 'turbojpeg' and 'turbojpeg-static' too"

Revert commit 74cc2e33 (FindJPEG: Search for 'turbojpeg' and
'turbojpeg-static' too, 2021-01-09, v3.20.0-rc1~176^2) pending further
investigation.  The "turbo" variants are not drop-in replacements on all
platforms.

Fixes: #22333