[ci] Refactor Circle config, remove sccache, and enable parallelism
[ci] Refactor Circle config, remove sccache, and enable parallelism

This work was inspired by #123. It refactors the Circle CI config to reduce
duplicate sections, removes the custom docker container and sccache setup, and
enables the main build workflow to run all three builds at the same time.

Closes: #908
Approved by: bmwill

aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core