The python docs say:

> New in version 3.7: text was added as a more readable alias for universal_newlines.

So the code introduced in commit 99cef05 (Remove duplicated version
detection code from waf/wscript) broke installs on python 3.6.

This is fixed by passing an explicit encoding, which also has the effect
of opening the pipe in text mode. This could have changed to
universal_newlines instead, but that name seems a bit confusing and does
not indicate that the result will be decoded into a string instead of
returning bytes, so using encoding seems better.

This is mostly needed for the `VERSION` file, which could contain
a trailing newline (e.g. vim always adds one unless you take effort to
prevent that). For good measure, the git describe output also has
whitespace stripped.

Only DATA_DIR and VERSION are actually used.

Removing LIB_DIR helps to make reproducible packages (presumably because
then there is no reference to the build machine architecture in the
resulting installed files, producing the same package regardless of
build machine), see
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1028310

For consistency, just remove the other unused variables too.

This check warned against using a very old dbus version that caused
breakage. However, the check used the `distutils` package for version
comparison, but that package is deprecated and will be removed in an
upcoming python version. Since there does not seem to be a direct
alternative for version comparisons in the core Python libraries and
this check is about a 4-year old dbus version anyway, just remove the
check rather than adding an extra dependency just for this.