libct/cap: no need to load capabilities

[kolyshkin]

We are not really interested in the capabilities of the current process, so there is no need to load those.

This results in some performance improvement since now the capability package don't have to parse /proc/self/status.

[lifubang]

Maybe we are interested in them in here:
https://github.com/moby/sys/blob/main/capability/capability_linux.go#L342-L346

[lifubang]

Maybe we are interested in them in here: https://github.com/moby/sys/blob/main/capability/capability_linux.go#L342-L346

I have no strong objection to merge this PR, but maybe in future we need to add it back to reduce the prctl(PR_CAPBSET_DROP) syscall.

[kolyshkin]

Maybe we are interested in them in here: https://github.com/moby/sys/blob/main/capability/capability_linux.go#L342-L346

In there it checks the bits that runc previously cleared and set itself. The values that are set by Load() are not used anywhere.

[kolyshkin]

Maybe we are interested in them in here: https://github.com/moby/sys/blob/main/capability/capability_linux.go#L342-L346

In there it checks the bits that runc previously cleared and set itself. The values that are set by Load() are not used anywhere.

To reiterate, no values from Load are used anywhere. @lifubang please take another look.

[lifubang]

LGTM, though I think it's useful to reduce prctl(PR_CAPBSET_DROP) syscall in future.
But let's leave future's things in the future.