Rollup merge of #64611 - alexcrichton:no-libstd-twice, r=Mark-Simulacrum

rustbuild: Don't package libstd twice

Looks like the packaging step for the standard library was happening
twice on CI, but it only needs to happen once! The `Analysis` packaging
step accidentally packaged `Std` instead of relying on compiling `Std`,
which meant that we ended up packaging it twice erroneously.