Omit the branch name when matching packages in manifest.json

[anvacaru]

Closes: #130
The kontrol package is defined in available_packages with a specific branch:

    GithubPackage('runtimeverification', 'kontrol', PackageName('kontrol'), branch='release'),

From the manifest.json, we can see that the kontrol entry looks like this:

{
  "kontrol": {
    "active": true,
    "attrPath": "packages.x86_64-linux.kontrol",
    "originalUrl": "github:runtimeverification/kontrol/acca16ffd6f4e693b7bda2dd8ca99eb335057dbe?narHash=...",
    "url": "github:runtimeverification/kontrol/acca16ffd6f4e693b7bda2dd8ca99eb335057dbe?narHash=..."
  },
}

When kup tries to match the installed packages with the available packages, it compares the repo_path (which includes the branch) with the url from the manifest (which does not include the branch). This mismatch causes kup to incorrectly conclude that kontrol is not installed.