Clean up BpfCoordinatorTest after refactors

Removed the use of a real IpServer instance in BpfCoordinatorTest,
as it is no longer needed after the refactors in aosp/2716773 and
aosp/3113123.

Test: atest TetheringTests
Bug: 294025403
Change-Id: I4760669372275a0165f4980705e328c80e0649a5
1 file changed