Remove metric icons from stats overview tab bar

[jkmassel]

Summary

• Drop the SF Symbol leading each metric tab (Views, Visitors, Likes, Comments, Posts) in MetricsOverviewTabView.
• Flatten the HStack wrapper in headerView now that only the label remains.

The icon added visual noise without carrying information beyond the uppercase label. showTrend still gates the trend badge below; only the header icon is removed.

Test plan

• Stats → Traffic tab: metric tab bar shows only the uppercase labels, no icons
• Selected metric underline + animation still works
• MetricsOverviewTabView preview renders correctly in Xcode

[dangermattic]

	1 Error
🚫	PR requires at least one label.

	2 Warnings
⚠️	View files have been modified, but no screenshot or video is included in the pull request. Consider adding some for clarity.
⚠️	PR is not assigned to a milestone.

Generated by 🚫 Danger

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress by scanning the QR code below to install the corresponding build.

	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	32059
	Version	PR #25508
	Bundle ID	org.wordpress.alpha
	Commit	97270ef
	Installation URL	5fbnpk81ienpo

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	32059
	Version	PR #25508
	Bundle ID	com.jetpack.alpha
	Commit	97270ef
	Installation URL	6o1g8god2lfcg

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.