chore: Remove STX opt in modal

[dan437]

Description

This recent PR enabled STX by default for new users and only hid the STX opt in modal. The purpose of this PR is to clean up unused code for the STX opt in modal.

Related issues

Fixes:

Manual testing steps

1. Install the extension from scratch
2. Be on Ethereum mainnet and have some funds there
3. You will not see any STX opt in modal

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 [2fc9426]

• 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 (1932 ± 54 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	1730	2167	1928	105	50
		domContentLoaded	1722	2048	1886	86	42
		load	1731	2175	1932	112	54
		domInteractive	18	98	57	22	10
		backgroundConnect	10	287	47	67	32
		firstReactRender	88	293	123	47	22
		getState	5	121	25	29	14
		initialActions	0	1	0	0	0
		loadScripts	1250	1548	1414	79	38
		setupStore	12	193	35	41	20
		uiStartup	1965	2745	2215	184	88

Bundle size diffs [🚀 Bundle size reduced!]

• background: -2 Bytes (-0.00%)
• ui: -5.41 KiB (-0.07%)
• common: -825 Bytes (-0.01%)

[metamaskbot]

Builds ready [6df2482]

• 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, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (2180 ± 163 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	382	3249	2079	515	247
		domContentLoaded	1755	3142	2140	327	157
		load	1773	3241	2180	340	163
		domInteractive	31	404	73	79	38
		backgroundConnect	9	97	36	24	12
		firstReactRender	52	172	110	31	15
		getState	4	70	25	22	11
		initialActions	0	1	0	0	0
		loadScripts	1287	2383	1599	271	130
		setupStore	10	68	31	21	10
		uiStartup	1973	3682	2428	393	189

Bundle size diffs [🚀 Bundle size reduced!]

• background: -2 Bytes (-0.00%)
• ui: -5.41 KiB (-0.07%)
• common: -825 Bytes (-0.01%)

[darkwing]

Thank you for the cleanup!