This commit drastically simplify the previous commit by removing
the layer variable syntax-checking-check-on-buffer-change and
the associated usage of it.
This effectively make spacemacs use the default flycheck setting.
If the user wants to customize this behavior then she can modify
directly the flycheck variable.
Add a variable `syntax-checking-check-on-buffer-change` to the
`syntax-checking` layer which conditionally sets the variable
`flycheck-check-syntax-automatically` to:
- `'(save mode-enabled)` when nil
- `'(save idle-change new-line mode-enabled)` (the package default)
when non-nil
The various settings determine when Flycheck evaluates the buffer:
- `save` triggers a buffer check after buffer save.
- `mode-enabled` triggers a buffer check when `flycheck-mode` is
enabled.
- `idle-change` triggers a buffer check after the editor has been idle
for `flycheck-idle-change-delay`
- `new-line` triggers a buffer check whenever a new line is inserted
into the buffer
