Consider removing cdx2cea_master from testthat subdirectory

[Smit-tay]

cdx2cea_master is the cause of most of the packages responsible for the devtools::check() warning:

Imports includes 21 non-default packages.
Importing from so many packages makes the package vulnerable to any of
them becoming unavailable.  Move as many as possible to Suggests and
use conditionally.

Perhaps do not include this project in the package any more.