Remove deprecated dpctl.tensor submodule

[ndgrigorian]

This PR removes the dpctl.tensor submodule, as it is migrated to dpnp as dpnp.tensor

This change makes dpctl a much smaller, lighter-weight package, with no built-in tensor capabilities. The memory sub-module and order_manager remain to support tensor-like extensions, but dpctl will focus on device management and providing a Python interface to SYCL implementations

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