textproc/py-pygments: Clean up BUILD_DEPENDS

from pyproject.toml:
[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

from CHANGES:

• Use Hatchling as a build backend instead of setuptools. This change is transparent to most users. Distribution packagers who build without build isolation need to add hatchling as a build dependency and remove setuptools. People downloading source distributions and wheels from PyPI directly should note that they now have `pygments in their file names instead of Pygments`. (#2573)

Reference: https://github.com/pygments/pygments/blob/master/pyproject.toml#L1-L3

		https://github.com/pygments/pygments/blob/master/CHANGES#L84-L89