Answer
Open the Google Dashboard on your phone and log in with the same Google account that you used while setting up the device. Select Android from the drop-down menu to get a list of all your devices with backup data. At the bottom is a button labeled Delete backup data, which removes all backed-up data from all devices.
How to delete Gmail Account Permanently with backup complete process
On your previous Android device, go to Settings > Privacy. On the Settings screen, check “Privacy.” Remove the check next to “Back Up My Data” from the menu. On the warning message that you’re about to delete your backup on Google servers, click OK.
Remove the “Backup and Sync” app from your dock. Delete the “Application Support/Google/Drive” folder as well as its contents. If you don’t want to sync all of your Google Drive folders, open the Google Drive folder on your computer and note all of the folders that you’ve designated to sync.
Go to System > Backup in the menu. Select “Back up to Google Drive” from the drop-down list. The account to which your phone will automatically back up is shown near the switch. You can see how long it’s been since your last backup below that.
Open the Google Photos app on your Android phone or tablet. To sign in to your Google Account, tap . Select the items you wish to remove from your Android device. Tap More Delete from Device in the top right corner.
Backups are stored in Android Backup Service and are limited to 5MB per app. According to Google’s Privacy Policy, this data is considered personal information. The user’s Google Drive backup data is limited to 25MB per app.
The answer is no—deleting an old iPhone backup from iCloud will not affect any of your data on your real iPhone. In fact, even deleting the backup of your current iPhone will have no effect on what’s really on it.