Replace if statement with call to Option::map

This CL replaces an if-statement with a call to the Option::map
function.  Having manual implementations of Option::map became a warning
with the 1.52.1 compiler update, and this was promoted to an error by
the build system.

Test: TH
Change-Id: I13e4adfbc84fbe855fd7d573e43e65bf602e0a5b
diff --git a/keystore2/src/super_key.rs b/keystore2/src/super_key.rs
index e02d9bc..bae18b0 100644
--- a/keystore2/src/super_key.rs
+++ b/keystore2/src/super_key.rs
@@ -126,10 +126,8 @@
     fn from_metadata(metadata: &BlobMetaData) -> Option<Self> {
         if let Some(EncryptedBy::KeyId(key_id)) = metadata.encrypted_by() {
             Some(SuperKeyIdentifier::DatabaseId(*key_id))
-        } else if let Some(boot_level) = metadata.max_boot_level() {
-            Some(SuperKeyIdentifier::BootLevel(*boot_level))
         } else {
-            None
+            metadata.max_boot_level().map(|boot_level| SuperKeyIdentifier::BootLevel(*boot_level))
         }
     }