fix: disable buy for btc testnet accounts

[montelaidev]

Description

This PR disables the Buy / sell button for btc testnet accounts

Related issues

Fixes: https://github.com/MetaMask/accounts-planning/issues/655

Manual testing steps

1. Create a testnet btc account
2. Go to the overview page
3. See that the buy/sell button is disabled.

Screenshots/Recordings

Before

After

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.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[metamaskbot]

Builds ready [8908e36]

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

Page Load Metrics (2331 ± 137 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	760	3191	2247	441	212
		domContentLoaded	1875	3168	2294	296	142
		load	1937	3185	2331	286	137
		domInteractive	21	79	53	17	8
		backgroundConnect	6	111	40	31	15
		firstReactRender	54	204	127	39	19
		getState	5	64	29	21	10
		initialActions	0	0	0	0	0
		loadScripts	1371	2238	1701	224	108
		setupStore	12	81	36	23	11
		uiStartup	2226	3587	2639	307	148

Bundle size diffs

• background: 0 Bytes (0.00%)
• ui: 347 Bytes (0.00%)
• common: 0 Bytes (0.00%)