Update Xcode schemes for the package

[lorentey]

These are used when we open the package folder in Xcode; they contain configuration settings (such as enabling code coverage collection) that is missing from Package.swift.

This update makes these stop referring to nonexistent targets and commit some changes that Xcode adds on its own every time we open the project.

Checklist

• I've read the Contribution Guidelines
• My contributions are licensed under the Swift license.
• I've followed the coding style of the rest of the project.
• I've added tests covering all new code paths my change adds to the project (if appropriate).
• I've added benchmarks covering new functionality (if appropriate).
• I've verified that my change does not break any existing tests or introduce unexplained benchmark regressions.
• I've updated the documentation if necessary.

[lorentey]

@swift-ci test

[matt795]

True