x11/kitty: Update to 0.30.0

• Add x11-fonts/roboto-fonts-ttf to build dependencies
• Add devel/xxhash to lib dependencies
• Use version 1.21 of go language
• Set up the variable PYTHONDONTWRITEBYTECODE in the build environment to fix the following error in poudriere:

>> Checking for filesystem violations... done

>> Error: Filesystem touched during build:

extra: usr/local/lib/python3.9/site-packages/_distutils_hack/__pycache__/__init__.cpython-39.opt-2.pyc

It's probably caused by sphinx when building docs.

• However, pass the option -OO to python command, in the build stage, so that we can install kitty's bytecode.
• Remove files/patch-docs_conf.rst

Release notes: https://sw.kovidgoyal.net/kitty/changelog/#id1