Jetpack: remove site registration nonce (step 1) (#42076)

Remove registration_nonce from site connection endpoint, and the JS API client that calls it.
We already have WP nonce in there, so another nonce is excessive and hinders our progress on other projects.

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/13553192029

Upstream-Ref: Automattic/jetpack@da18258

Author: sergeymitr

package.json

@@ -21,7 +21,7 @@
 	"dependencies": {
 		"@automattic/jetpack-analytics": "^0.1.36",
 		"@automattic/jetpack-components": "^0.67.1",
-		"@automattic/jetpack-connection": "^0.37.1-alpha",
+		"@automattic/jetpack-connection": "^0.38.0-alpha",
 		"@automattic/jetpack-script-data": "^0.2.1",
 		"@automattic/jetpack-shared-extension-utils": "^0.17.3",
 		"@automattic/popup-monitor": "1.0.2",