Remove lean4-keybinding-* user options and dissolve other parts of lean4-settings.el

[mekeor]

Lean4-Mode currently offers these variables:

(defcustom lean4-keybinding-std-exe1 (kbd "C-c C-x")
  "Main Keybinding for `lean4-std-exe'."
  :group 'lean4-keybinding :type 'key-sequence)
(defcustom lean4-keybinding-std-exe2 (kbd "C-c C-l")
  "Alternative Keybinding for `lean4-std-exe'."
  :group 'lean4-keybinding  :type 'key-sequence)
(defcustom lean4-keybinding-show-key (kbd "C-c C-k")
  "Lean Keybinding for `quail-show-key'."
  :group 'lean4-keybinding  :type 'key-sequence)
(defcustom lean4-keybinding-server-restart (kbd "C-c C-r")
  "Lean Keybinding for server-restart."
  :group 'lean4-keybinding  :type 'key-sequence)
(defcustom lean4-keybinding-tab-indent (kbd "TAB")
  "Lean Keybinding for `lean4-tab-indent'."
  :group 'lean4-keybinding  :type 'key-sequence)
(defcustom lean4-keybinding-auto-complete (kbd "S-SPC")
  "Lean Keybinding for auto completion."
  :group 'lean4-keybinding  :type 'key-sequence)
(defcustom lean4-keybinding-lean4-toggle-info (kbd "C-c C-i")
  "Lean Keybinding for `lean4-toggle-info'."
  :group 'lean4-keybinding  :type 'key-sequence)
(defcustom lean4-keybinding-lake-build (kbd "C-c C-p C-l")
  "Lean Keybinding for `lean4-lake-build'."
  :group 'lean4-keybinding :type 'key-sequence)
(defcustom lean4-keybinding-refresh-file-dependencies (kbd "C-c C-d")
  "Lean Keybinding for `lean4-refresh-file-dependencies'."
  :group 'lean4-keybinding :type 'key-sequence)

From an user perspective, these user-options feel out of place because they expect to change the default key bindings of a package by customizing the respective keymap directly. And from perspective of a Elisp developer working on Lean4-Mode, I'd also prefer to deal with a single keymap rather than above-mentioned user-options together with a function like lean4-set-keys that enables them. Thus, I propose to remove these user-options.

Secondly, I propose to completely dissolve the lean4-settings.el file, in the sense that each user-options that is defined there, should be moved to the Elisp file where it is used.