fix decode example of UnsecuredJWT

[maxarndt]

.decode() is a static function of the UnsecuredJWT class. Instantiating a new object and calling the function afterwards doesn't make sense and leads to an exception:

const payload = new jose.UnsecuredJWT.decode(unsecuredJwt, {
                ^

TypeError: jose.UnsecuredJWT.decode is not a constructor
    at file:https:///Users/maxarndt/Downloads/some-repo/utilities/jwt/unsecuredJWT.js:12:17
    at ModuleJob.run (node:internal/modules/esm/module_job:185:25)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:281:24)
    at async loadESM (node:internal/process/esm_loader:88:5)
    at async handleMainPromise (node:internal/modules/run_main:65:12)

Because of this the new operator should be removed from the examples.

[panva]

Thank you @maxarndt