Developer-config: remove superfluous quotations from CMAKE_PREFIX_PATH
requested to merge tjcorona/common-superbuild:developer-config-remove-superfluous-quotations into master
If CMAKE_PREFIX_PATH is set, then we set the exported CMAKE_PREFIX_PATH flag to be a list of two things and it needs quotations. Otherwise, there is no need to add quotations (and doing so results in a developer config file with too many quotations, resulting in a warning).