This reverts commit 29c78ce841 and all other fixes
that have been made afterwards.
The motivation is that use-package is seen by many as a replacement for
`require`. Is use-package always defer the loading of packages then is breaks
this use case, this does not respect POLA so even if it was making Spacemacs
loading faster (up to 3s faster on some startup on my machine) we just cannot
use it, it would be irresponsible. Spacemacs should be easy to use, loading
performance will come with time but it is not a priority.
It appears that 29c78ce changed `:defer t` to be the default for
use-package, and that previously the `treemacs` and
`treemacs-projectile` packages in treemacs/packages.el specified `:defer
t`, but *not* `treemacs-evil`. Restoring `:demand t` (previously the
default) to `treemacs-evil` appears to fix#10422.