Mtbroker to just broker it is cleaner

[vaikas]

Proposed Changes

• Back when we had the original broker I created mtbroker to distinguish. It's now been around for so long that it's safe to rename it to more clearer broker. mtbroker was just a different implementation, there's no need to carry that around in the name / package anymore (especially folks that don't know the history), it's just confusing. So change that.
• NOTE Not changing the brokerclass type, hence there are no user visible changes.

Release Note

Docs

[n3wscott]

/lgtm

Good job!

[codecov]

Codecov Report

Merging #5021 (a30e3a5) into master (e8bc8ed) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5021   +/-   ##
=======================================
  Coverage   83.09%   83.09%           
=======================================
  Files         283      283           
  Lines        7933     7933           
=======================================
  Hits         6592     6592           
  Misses        968      968           
  Partials      373      373           

Impacted Files	Coverage Δ
pkg/broker/filter/filter_handler.go	80.40% <ø> (ø)
pkg/broker/filter/stats_reporter.go	87.30% <ø> (ø)
pkg/broker/ingress/ingress_handler.go	62.76% <ø> (ø)
pkg/broker/ingress/stats_reporter.go	87.75% <ø> (ø)
pkg/broker/ttl.go	72.72% <ø> (ø)
pkg/reconciler/broker/broker.go	80.46% <ø> (ø)
pkg/reconciler/broker/config.go	86.66% <ø> (ø)
pkg/reconciler/broker/controller.go	93.02% <ø> (ø)
pkg/reconciler/broker/resources/channel.go	100.00% <ø> (ø)
pkg/reconciler/broker/resources/subscription.go	100.00% <ø> (ø)
... and 2 more

---

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[knative-metrics-robot]

The following is the coverage report on the affected files.
Say /test pull-knative-eventing-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/broker/filter/filter_handler.go	Do not exist	88.5%
pkg/broker/filter/stats_reporter.go	Do not exist	84.6%
pkg/broker/ingress/ingress_handler.go	Do not exist	78.0%
pkg/broker/ingress/stats_reporter.go	Do not exist	83.3%
pkg/broker/ttl.go	Do not exist	85.0%
pkg/reconciler/broker/broker.go	Do not exist	84.3%
pkg/reconciler/broker/config.go	Do not exist	93.3%
pkg/reconciler/broker/controller.go	Do not exist	88.9%
pkg/reconciler/broker/resources/channel.go	Do not exist	100.0%
pkg/reconciler/broker/resources/subscription.go	Do not exist	100.0%
pkg/reconciler/broker/trigger/controller.go	Do not exist	88.9%
pkg/reconciler/broker/trigger/trigger.go	Do not exist	86.1%

[vaikas]

/retest
another flake for rekt with 0.3

[n3wscott]

/lgtm
/approve

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: n3wscott

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• OWNERS [n3wscott]

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