Update supported chains

[vbaranov]

Motivation

Remove not hosted any more chains from supported_chains variable default values

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools

[coveralls]

Pull Request Test Coverage Report for Build b3537e8a-e850-47bf-bd39-7699495f56b4

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 15 unchanged lines in 6 files lost coverage.
• Overall coverage decreased (-0.2%) to 76.611%

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Files with Coverage Reduction	New Missed Lines	%
apps/block_scout_web/lib/block_scout_web/controllers/chain/market_history_chart_controller.ex	1	78.57%
apps/indexer/lib/indexer/fetcher/token.ex	1	80.0%
apps/indexer/lib/indexer/fetcher/token_balance.ex	2	87.88%
apps/indexer/lib/indexer/block/catchup/bound_interval_supervisor.ex	3	85.19%
apps/indexer/lib/indexer/block/fetcher.ex	4	86.75%
apps/indexer/lib/indexer/fetcher/token_instance.ex	4	0.0%

Totals
Change from base Build 5a34f4b0-f9e1-41c3-a00b-ad47a04e51c0:	-0.2%
Covered Lines:	5290
Relevant Lines:	6905

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💛 - Coveralls