It looks like soon after I started investigating scalar conversions for #14121 (but well before I made the PR) a major underlying hole was plugged in pyarrow via apache/arrow#36162. Most of #14121 was created to give us a way to handle scalars from pyarrow generically in libcudf. Now that pyarrow scalars can be easily tossed into arrays, we no longer really need separate scalar functions in libcudf; we can simply create an array from the scalar, put it into a table, and then call the table function.

Additionally, arrow also has a function for creating an array from a scalar. This function is not new but [was previously undocumented](apache/arrow#40373). The builder code added to libcudf in #14121 can be removed and replaced with that factory. The scalar conversion is as simple as calling that arrow function and then using our preexisting `from_arrow` function on the resulting array.

For now this PR is just a simplification of internals. Future PRs will remove the scalar API once we have a more standard path for the conversion of arrays via the C Data Interface.

Authors:
  - Vyas Ramasubramani (https://github.com/vyasr)

Approvers:
  - Yunsong Wang (https://github.com/PointKernel)
  - David Wendt (https://github.com/davidwendt)
  - Bradley Dice (https://github.com/bdice)

URL: #15213