Also remove the docstring about SPC h SPC as it is already implied for the other
options in the dotfile.
Note that this commit modifies one condition, namely disabled mode condition.
It removes the first test:
(not (spacemacs/mplist-get dotspacemacs-line-numbers :enabled-for-modes))
as it is not necessary since we have a `or` in the enable-p condition. Disabled
modes will be checked only if the current major mode is not explicitly enabled
(as intented).