Clean up files readily available from Slackware source mirrors

source/SlackBuild/borgbackup/README.md

@@ -27,7 +27,7 @@ Optional dependencies:
 - https://github.com/borgbackup/borg/issues/5591 we found in BorgBackup-1.1.15 that xxHash-0.8.0 is now preferred as the hash library instead of a built-in hash library. That means it depends on files not installed as part of the BorgBackup package installation. During compilation of BorgBackup, it checks a Boolean https://github.com/borgbackup/borg/blob/1.1.15/setup.py#L26 and also looks for installed copies of xxHash (and its library libxxhash) to determine if this "better" library should be used or if the bundled hash library should be used. If 
 - This same "check the system if this package is installed, otherwise use the bundled version" applies to `lz4`, `libstd`, and `libb2` (blake2). It should be noted that if BorgBackup is compiled while the system library is used but the compiled package is then moved to a system such as Unraid without that installed package, an error such as `libxxhash.so.0: cannot open shared object file: No such file or directory` may be seen. This particular error was seen when running `borg --version` on a system without the `xxhash` library installed. I downloaded the library from a Slackware source mirror: http://slackware.cs.utah.edu/pub/slackware/slackware64-current/slackware64/l/
 - I updated the SlackBuild to adjust these flags in the `setup.py` file to False (default is True) to force usage of the bundled libraries for maximum portability between Slackware and the super-cut-down Unraid flavor of Slackware. This way, Unraid users of this package need not install extra packages such as `xxHash` to get BorgBackup working.
-- There were some other files in this SlackBuild directory such as acl-2.2.53, cryptography-2.8, libffi-3.2.1, lz4-1.9.2, and msgpack-python-0.6.2. I found that msgpack-python and cryptography were not installed on my build system, but when I compiled the package I did have libffi-3.3, acl-2.2.53, and lz4-1.9.3 installed so I left those in the build folder.
+- There were some other files in this SlackBuild directory such as acl-2.2.53, cryptography-2.8, libffi-3.2.1, lz4-1.9.2, and msgpack-python-0.6.2. I found that msgpack-python and cryptography were not installed on my build system, but when I compiled the package I did have libffi-3.3, acl-2.2.53, and lz4-1.9.3 installed. They were installed by default with Slackware, and if needed can be downloaded from http://slackware.cs.utah.edu/pub/slackware/slackware64-current/slackware64/l/.
 - I confirmed that Unraid did NOT have libffi, lz4, acl, cryptography, xxHash or msgpack installed by default.
 - The original README noted that, in order for documentation to be generated, both Sphinx and `sphinx_rtd_theme` needed to be installed. However, during compilation I ran into an error `No module named 'guzzle_sphinx_theme'` and then also needed to install https://pypi.org/project/guzzle_sphinx_theme/ with `pip3 install guzzle_sphinx_theme`. After that, I was able to complete the compilation.
 - My list of Pip3 packages (with Python 3.9.1) at the time of compilation was `-lxc=0.1, alabaster=0.7.12, appdirs=1.4.4, Babel=2.9.0, Brotli=1.0.9, caca=0.99b19, certifi=2020.12.5, chardet=4.0.0, cupshelpers=1.0, Cython=0.29.21, distro=1.5.0, docutils=0.16, future=0.18.2, getmail6=6.11, gpg=1.15.0, guzzle-sphinx-theme=0.7.11, gyp=0.1, idna=2.10, imagesize=1.2.0, include-server=3.3.3, isc=2.0, Jinja2=2.11.2, lensfun=0.3.95, libwebp=0.0, llfuse=1.3.8, M2Crypto=0.37.1, Mako=1.1.3, MarkupSafe=1.1.1, mercurial=5.6.1, meson=0.56.0, netsnmp-python=1.0a1, notify2=0.3.1, packaging=20.8, Pillow=8.0.1, pip=20.3.3, ply=3.11, pssh=2.3.4, pwquality=1.4.4, pycairo=1.20.0, pycups=2.0.1, pycurl=7.43.0.6, Pygments=2.7.3, PyGObject=3.38.0, pyparsing=2.4.7, PyQt4-sip=4.19.23, PyQt5=5.15.2, PyQt5-sip=12.8.1, pysol-cards=0.10.1, python-sane=2.8.3, pytz=2020.5, pyxdg=0.27, QScintilla=2.11.6, random2=1.0.1, requests=2.25.1, rpm=4.16.1.2, SCons=4.0.1, setuptools=51.1.0, sip=5.5.0, six=1.15.0, snowballstemmer=2.0.0, Sphinx=3.4.1, sphinx-rtd-theme=0.5.0, sphinxcontrib-applehelp=1.0.2, sphinxcontrib-devhelp=1.0.2, sphinxcontrib-htmlhelp=1.0.3, sphinxcontrib-jsmath=1.0.1, sphinxcontrib-qthelp=1.0.3, sphinxcontrib-serializinghtml=1.1.4, toml=0.10.2, undervolt=0.3.0, urllib3=1.26.2`