Convert all uses of base::TimeDelta to std::chrono::microseconds

- TimeDelta has different constructors for libchrome in aosp and
  chromeos, causing a lot of preprocessor switches
- TimeDelta internally saves the time in microseconds,
  std::chrono::microseconds is the logical replacement

Bug: 317116676
Test: m com.android.btservices
Flag: EXEMPT, mechanical refactor
Change-Id: I099e5b7a9993e2bfce2cd2d59ede9b07179c2be8