refactor: remove null check in register.ts options.base

Inside registerServiceWorker, we were originally using the nullash coalescing
operator to check if options.base was null or undefined. However, I realized
this check is not necessary.

If you look at getOptions' return value, we return an object with a key "base"
which is of type "string". We get that value by calling resolveBase which always
returns a string.

As a result, we didn't need to check if options.base was null or undefined
because it never can be.

test/unit/register.test.ts

@@ -105,7 +105,6 @@ describe("register", () => {
       const location: LocationLike = {
         pathname: "",
         origin: "http://localhost:8080",
-        // search: "?environmentId=600e0187-0909d8a00cb0a394720d4dce",
       }
       const { window } = new JSDOM()
       global.window = (window as unknown) as Window & typeof globalThis