Unpin conda-build

[jclarkeSTFC]

The PR that fixed the massive logs problem has been merged in to conda-build, so the pin can hopefully be removed.

See #36544 for the original pin to avoid massive logs. The issue (conda/conda-build#5106) was fixed in conda-build with conda/conda-build#5108.

Fixes #36551.

To test:

Check that the size of the build logs is similar to those with the pin still in.

This does not require release notes because it only affects build logs

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[thomashampson]

Packaging environment now installs conda-build 3.28.4, which resolves the issue with huge logs. We can now remove the pin without worrying about clogging up the build servers.