Undo heading levels in PSA APIs

Undo heading levels because these are APIs, which live at a different level in this option.

Author: AnotherButler

docs/api/storage/psa_internal_storage.md

@@ -1,4 +1,4 @@
-### PSA internal storage
+## PSA internal storage
 
 PSA internal storage APIs enable saving data to and retrieving data from a PSA internal flash.
 
@@ -7,11 +7,11 @@ The implementation of PSA internal storage varies depending on the target type:
 - On a single core ARMv7-M target, PSA internal storage APIs are implemented by calling the default internal TDBStore instance.
 - On PSA targets that implement Secure Partition Manager (SPM), PSA internal storage is implemented as a secure service. The service uses an access control list to ensure that it only accesses entries created from the Non-Secure Processing Environment (NSPE).
 
-#### PSA internal storage class reference
+### PSA internal storage class reference
 
 [![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/development/mbed-os-api-doxy/psa__prot__internal__storage_8h.html)
 
-#### Related content
+### Related content
 
 - [API specification in Mbed OS](../apis/storage.html).
 - [PSA secure storage](https://pages.arm.com/PSA-APIs).

docs/api/storage/psa_protected_storage.md

@@ -1,14 +1,14 @@
-### PSA protected storage
+## PSA protected storage
 
 PSA protected storage APIs enable saving data to and retrieving data from PSA protected storage.
 
 Unlike [PSA internal storage](../apis/psa-internal-storage.html), PSA protected storage always runs on the NSPE side and redirects calls to the KVStore instance.
 
-#### PSA protected storage class reference
+### PSA protected storage class reference
 
 [![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/development/mbed-os-api-doxy/protected__storage_8h.html)
 
-#### Related content
+### Related content
 
 - [API specification in Mbed OS](../apis/storage.html).
 - [PSA Secure Storage](https://pages.arm.com/PSA-APIs).