fix: remove legacy REST endpoints for broadcast & encode (v0.44.x)

[clevinson]

Description

This PR removes legacy REST endpoints for broadcast & encode in order for #10029 to be backported successfully to v0.44 (#10034).

It is essentially a partial backport of #9594 which removed all legacy REST endpoints (already merged on master).

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[robert-zaremba]

utACK

[robert-zaremba]

There are few tests failing, I will check them

[orijbot]

Visit https://dashboard.github.orijtech.com?back=0&pr=10041&remote=false&repo=cosmos%2Fcosmos-sdk to see benchmark details.

[robert-zaremba]

I was trying to fix the tests in x/auth/client/rest/rest_test.go in the end I removed it: 1cfa714

[colin-axner]

Looks like I can remove this test on ibc-go which we were hosting for the sdk. Our sdk_test.go folder contains test we needed to migrate with us since they required IBC to test certain cases. Just want to double check I follow these changes correctly. Looks like this test can be removed as well