devel/libgudev: Update to 233

Update devel/libgudev to 233. [1]
Change to use MASTER_SITE_GNOME.
Disable umockdev since we don't have that in ports, and it's only used for
tests.
Fix COMMENT per portlint.

PR: 248565 [1]
Requested by: jbeich [1]
MFH: 2020Q3