Change socket mount paths to the default locations as used by Spire images

[marcofranssen]

To prepare for #209 we should change the socket mount paths to default to the paths images are configured for.

See https://github.com/spiffe/spire/blob/main/Dockerfile#L33-L54 for the various paths in the images that can run with the non-root user 1000.

Probably also remove the option to configure them. Originally I created those values to remove duplication of defining socket paths. Thinking about that now I should have used a macro like we are doing now with the spire-lib ones.