Revert "[musicdb] more curl fixes"

This reverts commit 4995c010b67ec20a7f46d0bc08eee5703763bcdb.
Revert "[musicdb] fix the curlfile crash on exit properly this time"

This reverts commit b63bcc3d4dae8ed5404f71bdb2abbc485526eb45.
Revert "[musicdb] fix: avoid crash on exit in curl rate-limiter due to iterator invalidation"

This reverts commit 02f76a216a68f552777caa80b2bd6b0f08de31df.
Revert "[musicdb] implement a per host rate-limiter to avoid hitting the musicbrainz rate-limit and be more friendly to our peers."

This reverts commit 241a4fc0babb108f652b993b2b40a20397433118.
Merge pull request #2726 from ulion/revert_curl_ratelimit

Revert curl ratelimit