Improve warning "Flag --all.xxx has been deprecated, Deprecated"

[jsteemann]

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I used a recent version of the starter (from 3.10.0 packages) to start a single server with the following command:

arangodb --starter.mode single --starter.data-dir myDir  --all.temp.intermediate-results-path "temp" --all.use-splice-syscall false  

Starting the arangod server instance worked, but the first 2 lines of output were:

Flag --all.temp.intermediate-results-path has been deprecated, Deprecated
Flag --all.use-splice-syscall has been deprecated, Deprecated

These message comes from ./vendor/github.com/spf13/pflag/flag.go.

Unfortunately the messages are not very helpful for end users. Can they be improved somehow? I guess the intention is to tell the end user to not use --all.*, but something else. But it is unclear what exactly.