Repository: firebase/firebase-ios-sdk (language: cpp)

Issue:
Something in Firebase prevents from updating to Firebase/AdMob ~> 8.3.0
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### [REQUIRED] Step 1: Describe your environment

  * Xcode version: 12.4 (12D4e)
  * Firebase SDK version: 7.9.0
  * Installation method: `CocoaPods`
  * Firebase Components: (Auth, Core, Database, Storage, Crashlytics, Analytics, AdMob)

### [REQUIRED] Step 2: Describe the problem

#### Steps to reproduce:

I've got messages that I should upgrade Google AdMob SDK to V8.
I've started with upgrading All Firebase dependencies to the most up-to-date version (7.9.0), worked fine.
Now when running `pod outdated` I'm getting this:
```
Google-Mobile-Ads-SDK 7.69.0 -> 7.69.0 (latest version 8.3.0)
```
When trying to force this to be 8.3.0 I'm getting this:
```
[!] CocoaPods could not find compatible versions for pod "Firebase/Analytics":
  In Podfile:
    Firebase/Analytics (~> 7.9.0)

None of your spec sources contain a spec satisfying the dependency: `Firebase/Analytics (~> 7.9.0)`.

You have either:
 * out-of-date source repos which you can update with `pod repo update` or with `pod install --repo-update`.
 * mistyped the name or version.
 * not added the source repo that hosts the Podspec to your Podfile.
```

Tried comment out `Firebase/Analytics` and got the same error on `Firebase/Crashlytics` and so on about `Firebase/Auth` etc.

**Bottom line:**
It seems like `Firebase/AdMob` newest version doesn't compatible with other `Firebase` repos.

#### Relevant Code:

Podfile:
```
	pod 'Firebase/Core', '~> 7.9.0'
	pod 'Firebase/Storage', '~> 7.9.0'
	pod 'Firebase/Database', '~> 7.9.0'
	pod 'Firebase/Auth', '~> 7.9.0'
	pod 'Firebase/Crashlytics', '~> 7.9.0'
	pod 'Firebase/Analytics', '~> 7.9.0'
	pod 'Firebase/AdMob' #, '~> 7.69.0'
	pod 'SDWebImage', '~> 5.6.1'
	pod 'FirebaseUI/Storage', '~> 9.0.0'
	pod 'GoogleSignIn' #, '~> 5.0.2'
```



Discussion / hints:
I found a few problems with this issue:
  * I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.
  * This issue does not seem to follow the issue template. Make sure you provide all the required information.
tl;dr: Replace `pod 'Firebase/AdMob'` with `pod 'Google-Mobile-Ads-SDK'`.

Background, see docs at https://firebase.google.com/docs/ios/setup?authuser=0#initialize-firebase. Usage of `Firebase/AdMob` is no longer recommended since `Google-Mobile-Ads-SDK` releases at a different cadence than the other Firebase subspecs. It is especially exacerbated right now since `Google-Mobile-Ads-SDK` recently did a breaking change major release. 

The next Firebase major release will either update the `Admob` subspec to 8.x or completely remove it.
Got it, thanks.
Great! I'll leave this issue open to track making the Firebase podspec update for the 8.0.0 release.
Current plan is to remove the Firebase/AdMob subspec in favor of directly using the `Google-Mobile-Ads-SDK` podspec.

Fix patch:
diff --git a/Firebase.podspec b/Firebase.podspec
index 122716587a1..5f6bf5a3412 100644
--- a/Firebase.podspec
+++ b/Firebase.podspec
@@ -83,12 +83,6 @@ Simplify your app development, grow your user base, and monetize more effectivel
     ss.watchos.deployment_target = '6.0'
   end
 
-  s.subspec 'AdMob' do |ss|
-    ss.dependency 'Firebase/CoreOnly'
-    ss.ios.deployment_target = '9.0'
-    ss.ios.dependency 'Google-Mobile-Ads-SDK', '~> 7.66'
-  end
-
   s.subspec 'AppDistribution' do |ss|
     ss.dependency 'Firebase/CoreOnly'
     ss.ios.dependency 'FirebaseAppDistribution', '~> 7.11.0-beta'
diff --git a/FirebaseCore/CHANGELOG.md b/FirebaseCore/CHANGELOG.md
index 0a4729dc4ca..fecbeb0eac3 100644
--- a/FirebaseCore/CHANGELOG.md
+++ b/FirebaseCore/CHANGELOG.md
@@ -1,3 +1,7 @@
+# Firebase 8.0.0
+- [removed] The `Firebase/AdMob` CocoaPods subspec has been removed. Use the `Google-Mobile-Ads-SDK`
+  CocoaPod instead. (#7833)
+
 # Firebase 7.10.0
 - [changed] Update Nanopb to version 0.3.9.8. It fixes a possible security issue. (#7787)
 


Test patch: