Remove autorest core version from build scripts

[jhendrixMSFT]

The code generator MUST be the ONLY source of this value.

• The purpose of this PR is explained in this or a referenced issue.
• The PR does not update generated files.
  • These files are managed by the codegen framework at Azure/autorest.go.
• Tests are included and/or updated for code changes.
• Updates to CHANGELOG.md are included.
• MIT license headers are included in each file.