Delete statsd

[pingles]

Inspired by #429 and other deprecation tidy-up, I thought this would be a good thing to consider.

I think it tidies up nicely.

[pingles]

@Joseph-Irving what do you think?

[codecov]

Codecov Report

Merging #431 into master will increase coverage by 0.95%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #431      +/-   ##
==========================================
+ Coverage   45.14%   46.09%   +0.95%     
==========================================
  Files          26       26              
  Lines        1070     1050      -20     
==========================================
+ Hits          483      484       +1     
+ Misses        532      514      -18     
+ Partials       55       52       -3     

Impacted Files	Coverage Δ
pkg/aws/metadata/handler_credentials.go	83.72% <ø> (+3.72%)	⬆️
pkg/aws/metadata/handler_health.go	73.17% <ø> (+3.40%)	⬆️
pkg/aws/metadata/handler_role_name.go	84.31% <ø> (+3.18%)	⬆️
pkg/aws/sts/gateway.go	51.02% <ø> (+2.00%)	⬆️
pkg/server/gateway.go	0.00% <ø> (ø)
pkg/server/server.go	21.73% <ø> (+0.90%)	⬆️
pkg/server/tls.go	46.57% <0.00%> (+0.68%)	⬆️

[Joseph-Irving]

lgtm, Prometheus is the metrics standard these days, don't see any reason to carry this into v4.