Drop UCX pinning

[jakirkham]

Previously RAPIDS libraries directly depended on UCX. As a result it made sense to align UCX versions in the different libraries and the metapackage. However now that UCXX is used throughout RAPIDS and only UCXX depends on UCX, this top-level UCX pinning is no longer relevant. So we should drop it.

integration/conda/recipes/rapids/recipe.yaml

Line 49 in 3ca79d0

- conda-forge::ucx ${{ ucx_version }}

integration/conda/recipes/versions.yaml

Lines 15 to 16 in 3ca79d0

	ucx_version:
	- '>=1.15.0,<1.20.0'

Also this would be a good opportunity to explicitly add UCXX to the metapackage.