Remove CURL, master branch (2019.01.18.)

Removed the usage of FindCURL.cmake from CollectionUtilities.

The package probably did use CURL at one point of its file, but it doesn't use it by now. So there's no need for it to set it up for its build.

Note that this is why the current CentOS 7 nightlies don't show a build error, even though they fail to find CURL.

http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/GITWebArea/nightlies/master/2019-01-17T2139/Athena/x86_64-centos7-gcc8-opt/Athena/cmake_config.log.html

-- Could NOT find CURL (missing: CURL_LIBRARY CURL_INCLUDE_DIR)

Since as ATLINFR-2820 explains, this becomes an error with CMake 3.13, the simplest was just to remove this unneeded dependency from the CollectionUtilities package.