Reworded the DELETE (previous DROP) key function in Architecture chapter

Readded the DELETE key function based on 1257 in Architecture chapter
where we also update from DROP to DELETE.

Author: Andriciuc

contrib/pg_tde/documentation/docs/architecture/index.md

@@ -293,15 +293,23 @@ With `pg_tde.inherit_global_key_providers`, it is also possible to set up a defa
 
 With this feature, it is possible for the entire database server to easily use the same principal key for all databases, completely disabling multi-tenency.
 
-A default key can be managed with the following functions:
+#### Manage a default key
 
-```sql
-pg_tde_set_default_key_using_global_key_provider('key-name', 'provider-name', 'true/false')
-```
+You can manage a default key with the following functions:
+
+* `pg_tde_set_default_key_using_global_key_provider('key-name','provider-name','true/false')`
+* `pg_tde_delete_principal_key()`
+
+!!! note
+    `pg_tde_delete_principal_key()` is only possible if there's no table currently using the default principal key.
+    Changing the default principal key will rotate the encryption of internal keys for all databases using the current default principal key.
+
+#### Deleting the key
 
-`DROP` is only possible if there's no table currently using the default principal key.
+The `pg_tde_delete_principal_key()` function removes the principal key for the current database. If the current database has any encrypted tables, and there isn’t a default principal key configured, it reports an error instead. If there are encrypted tables, but there’s also a global default principal key, internal keys will be encrypted with the default key.
 
-Changing the default principal key will rotate the encryption of internal keys for all databases using the current default principal key.
+!!! note
+    WAL keys **cannot** be deleted, as server keys are managed separately.
 
 ### Current key details