chore: Remove obsolete keys

[Gudahtt]

Description

Remove references to obsolete keys.

• PUBNUB_*: These were used for the old mobile state sync feature, which was removed a long time ago.
• ETHERSCAN_KEY: This was used for incoming transactions, but we've since switched to our own API.
• OPENSEA_KEY: We've switched to Reservoir

The ETHERSCAN_KEY environment variable is still refrenced in the gridplus-sdk package, so it has been left in the build.yml file as null to indicate that it's intentionally unset.

Related issues

N/A

Manual testing steps

N/A

Screenshots/Recordings

N/A

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[Gudahtt]

This was still being set, but it did nothing: https://github.com/MetaMask/core/blob/f8e5f2e3cadecc44c1c5b40b3ed3c36d154346cb/packages/assets-controllers/src/NftController.ts#L1382

(see that the key isn't used anywhere).

[Gudahtt]

It's not being exfiltrated or anything. Gridplus optionally uses it to fetch contract calldata from Etherscan.

[metamaskbot]

Builds ready [2069269]

• builds: chrome, firefox
• builds (beta): chrome
• builds (flask): chrome, firefox
• builds (MMI): chrome, firefox
• builds (test): chrome, firefox
• builds (test-flask): chrome, firefox
• build viz: Build System
• mv3: Background Module Init Stats
• mv3: UI Init Stats
• mv3: Module Load Stats
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• code coverage: Report
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5, 6
  • common: 0, 1, 10, 11, 12, 2, 3, 4, 5, 6, 7, 8, 9
  • content-script: 0
  • offscreen: 0
  • ui: 0, 1, 10, 11, 12, 13, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (1938 ± 121 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	414	2540	1781	518	249
		domContentLoaded	1473	2410	1903	248	119
		load	1529	2453	1938	252	121
		domInteractive	26	99	53	20	10
		backgroundConnect	9	92	33	22	10
		firstReactRender	17	98	42	25	12
		getState	5	89	31	26	12
		initialActions	0	0	0	0	0
		loadScripts	1069	1913	1456	207	99
		setupStore	6	59	16	17	8
		uiStartup	1753	3064	2228	341	164

Bundle size diffs [🚀 Bundle size reduced!]

• background: -35 Bytes (-0.00%)
• ui: 0 Bytes (0.00%)
• common: 0 Bytes (0.00%)