All touched Python scripts already assume and require UTF8, so manually
specifying encoding or decoding for functions in the subprocess module
is redundant to just using text=True, which exists since Python 3.7
The encoding arg is confusing, because it is not applied consistently
for all IO.
Also, it is useless, as the majority of files are ASCII encoded, which
are fine to encode and decode with any mode.
Moreover, UTF-8 is already required for most scripts to work properly,
so setting the encoding twice is redundant.
So remove the encoding from most IO. It would be fine to remove from all
IO, however I kept it for two files:
* contrib/asmap/asmap-tool.py: This specifically looks for utf-8
encoding errors, so it makes sense to sepecify the utf-8 encoding
explicitly.
* test/functional/test_framework/test_node.py: Reading the debug log in
text mode specifically counts the utf-8 characters (not bytes), so it
makes sense to specify the utf-8 encoding explicitly.
Bash is discouraged, and there was never a need to write locale
dependent Bash.
So remove the option and clarify that the LC_ALL settings enable UTF-8
mode in Python.
Mostly changes to remove src/univalue exceptions from the various linters,
and the required code changes to make them happy. As well as minor doc
changes.
