Remove ExperimentalEmbeddedPaymentElementApi.

[jaynewstrom-stripe]

Summary

We're moving embedded to GA!

Launch info here: https://home.corp.stripe.com/compass/projects/embedded-mobile-payment-element/launch_readiness?token=review_S72ARWcFaabp1x

[github-actions]

Diffuse output:

OLD: identity-example-release-base.apk (signature: V1, V2)
NEW: identity-example-release-pr.apk (signature: V1, V2)

          │          compressed          │         uncompressed         
          ├───────────┬───────────┬──────┼───────────┬───────────┬──────
 APK      │ old       │ new       │ diff │ old       │ new       │ diff 
──────────┼───────────┼───────────┼──────┼───────────┼───────────┼──────
      dex │   2.1 MiB │   2.1 MiB │  0 B │   4.3 MiB │   4.3 MiB │  0 B 
     arsc │     1 MiB │     1 MiB │  0 B │     1 MiB │     1 MiB │  0 B 
 manifest │   2.3 KiB │   2.3 KiB │  0 B │     8 KiB │     8 KiB │  0 B 
      res │ 302.9 KiB │ 302.9 KiB │  0 B │   457 KiB │   457 KiB │  0 B 
   native │   6.2 MiB │   6.2 MiB │  0 B │  15.8 MiB │  15.8 MiB │  0 B 
    asset │   7.7 KiB │   7.7 KiB │  0 B │   7.4 KiB │   7.4 KiB │  0 B 
    other │  95.7 KiB │  95.7 KiB │ -6 B │ 183.5 KiB │ 183.5 KiB │  0 B 
──────────┼───────────┼───────────┼──────┼───────────┼───────────┼──────
    total │   9.8 MiB │   9.8 MiB │ -6 B │  21.8 MiB │  21.8 MiB │  0 B 

 DEX     │ old   │ new   │ diff      
─────────┼───────┼───────┼───────────
   files │     1 │     1 │ 0         
 strings │ 20668 │ 20668 │ 0 (+0 -0) 
   types │  6493 │  6493 │ 0 (+0 -0) 
 classes │  5259 │  5259 │ 0 (+0 -0) 
 methods │ 31489 │ 31489 │ 0 (+0 -0) 
  fields │ 18221 │ 18221 │ 0 (+0 -0) 

 ARSC    │ old  │ new  │ diff 
─────────┼──────┼──────┼──────
 configs │  164 │  164 │  0   
 entries │ 3646 │ 3646 │  0

APK

   compressed    │   uncompressed   │                        
──────────┬──────┼───────────┬──────┤                        
 size     │ diff │ size      │ diff │ path                   
──────────┼──────┼───────────┼──────┼────────────────────────
 29.2 KiB │ -5 B │  64.6 KiB │  0 B │ ∆ META-INF/CERT.SF     
 25.9 KiB │ -1 B │  64.5 KiB │  0 B │ ∆ META-INF/MANIFEST.MF 
──────────┼──────┼───────────┼──────┼────────────────────────
 55.1 KiB │ -6 B │ 129.1 KiB │  0 B │ (total)