[services] Tunnelbroker - Removing a duplicate condition from waitUntilReady

Summary: This diff is a small follow-up from the landed D4741 comment to remove a duplicate condition from waitUntilReady() function which is covered by the while condition.

Test Plan:
Docker:
Run yarn run-tunnelbroker-service successfully built.

Nix:
Run nix develop, cd services/tunnelbroker, rm -dfr build && cmake -B build . && make -C build -j4. Expect successfully building the app.

Reviewers: tomek, karol

Reviewed By: tomek

Subscribers: ashoat, tomek, atul, karol, abosh

Differential Revision: https://phab.comm.dev/D4897