issue https://github.com/composer/composer/issues/3744
summary of changes
- replaced bin script "fetch-spdx-identifiers" by "update-spdx-licenses"
- "update-spdx-licenses" uses "Composer/Util/SpdxLicensesUpdater" to update "spdx-licenses.json" file with license identifier, fullname and osi-approved-status
- dropped "spdx-identifiers.json" (identifiers only)
- dropped "SpdxLicenseIdentifier", it's just "SpdxLicense" now
- modified "ShowCommand" to output the license with metadata and removed some unused method arguments (cleanup)