[lib] Remove extraneous ternary from threadUIName in thread-utils

Summary: This ternary's condition and expression if true are the same, so it can be replaced with an ||. Note that the cases still remain the same (the most notable being if threadInfo.name === '', then the expression if false is still chosen since '' is falsy).

Test Plan: Flow, close reading

Reviewers: atul

Reviewed By: atul

Subscribers: ashoat, palys-swm, Adrian

Differential Revision: https://phab.comm.dev/D4357