Reader: Remove curent featured image

[kean]

This is first part of CMM-1999: Reader: Adaptive Post Details Page. It removes the current featured image implementation, which is quite complex, to make the review easier.

[dangermattic]

	1 Warning
⚠️	View files have been modified, but no screenshot or video is included in the pull request. Consider adding some for clarity.

Generated by 🚫 Danger

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[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	31842
	Version	PR #25464
	Bundle ID	com.jetpack.alpha
	Commit	63d18c8
	Installation URL	1e64tsphr0k8g

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 WordPress by scanning the QR code below to install the corresponding build.

	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	31842
	Version	PR #25464
	Bundle ID	org.wordpress.alpha
	Commit	63d18c8
	Installation URL	0p7tjpfqrrj6o

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

[wpmobilebot]

Version 26.9 has now entered code-freeze, so the milestone of this PR has been updated to 27.0.