nuget with license file behaves different with enabled github resolve

[trivalik]

When I create a nuget package with <license type="file">LICENSE.txt</license> it automatically add the in nuspec the line <licenseUrl>https://aka.ms/deprecateLicenseUrl</licenseUrl>.

If --enable-github-licenses is enabled, then no license information is print into BOM.`

Without --enable-github-licenses, it prints out:

      "licenses": [
        {
          "license": {
            "name": "Unknown - See URL",
            "url": "https://aka.ms/deprecateLicenseUrl"
          }
        }
      ],

[mus65]

Opened #1011