feat(wallet): disable EIP-1559 on Polygon and Avalanche

[onyb]

Our current EIP-1559 gas oracle queries the Etherscan API, which only
supports Ethereum mainnet. As a result, priority fee estimations on
custom networks use results for Ethereum mainnet, which can either
result in transactions being stuck in the mempool forever, or in
over-payment of gas fees.

This commit will be reverted in brave/brave-browser#20469.

Resolves brave/brave-browser#20652.

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally: npm run test -- brave_browser_tests, npm run test -- brave_unit_tests, npm run lint, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Demo

Before	After
Screen.Recording.2022-01-24.at.6.17.57.PM.mov	Screen.Recording.2022-01-24.at.6.15.15.PM.mov

[bbondy]

otherwise lgtm

[yrliou]

LGTM

[srirambv]

Verification passed on

Brave	1.36.73 Chromium: 98.0.4758.66 (Official Build) nightly (arm64)
Revision	db1b4001d5ce29f141297f260d2b778e000b85a3-refs/branch-heads/4758@{#762}
OS	macOS Version 12.1 (Build 21C52)

• Verified EIP-1559 gas pricing is removed for Polygon

11968.mov