Fix byte-compile and package-lint errors as mentionned here
https://github.com/melpa/melpa/pull/7790#issuecomment-962727545
Fix a docstring that was too long, quoted `eshell-info-banner' in
three other docstrings.
Renaming functions may have introduced some breaking changes, hence
the update on the REAME. Since these were breaking changes, this
commit removes two functions as well which weren’t used internally
anymore.
eshell-info-banner will now default to duf if it is installed and
avaliable on the system, otherwise it will default to
platform-specific implementation.
