__git_cl_all_commands is used to cache the result of
__git_cl_commands(), but the actual code wasn't using it and was calling
the function everytime instead.

Change-Id: Ia2ce32b7de2812349808ec9aceeacf5adf463700
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2190337Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Henrique Ferreiro <hferreiro@igalia.com>