Revert session tracker to use std time package

[anjmao]

Compilation with xgo to build macOS doesn't work because it can't find needed syscall. Need to investigate xgo image. Also added TODO for windows since implementation need to be changed, but after Windows compilation is fixed (separate PR).

[codecov-io]

Codecov Report

Merging #1833 into master will decrease coverage by 0.05%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #1833      +/-   ##
==========================================
- Coverage   46.87%   46.82%   -0.06%     
==========================================
  Files         284      284              
  Lines       11651    11651              
==========================================
- Hits         5461     5455       -6     
- Misses       5768     5772       +4     
- Partials      422      424       +2

Impacted Files	Coverage Δ
session/pingpong/factory.go	0% <0%> (ø)	⬆️
session/time_tracker.go	100% <100%> (ø)	⬆️
tequilapi/sse/sse.go	71.11% <0%> (-5.56%)	⬇️
communication/nats/dialog/dialog_waiter.go	86.11% <0%> (-2.78%)	⬇️
core/discovery/discovery.go	66.38% <0%> (+0.84%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2cb1541...4e57027. Read the comment docs.