Clear SDK cache properly (#4396)

* Use close() instead of destroy, because close() is synchronized.

* Use new method to clear the SDK cache.

* Format file.

* Remove the legacy way to clear the SDK cache.

* Remove unused import

* revert name change

libraries/matrix/test/src/main/kotlin/io/element/android/libraries/matrix/test/FakeMatrixClient.kt

@@ -167,7 +167,7 @@ class FakeMatrixClient(
         return 0
     }
 
-    override suspend fun clearCache() {
+    override suspend fun clearCache() = simulateLongTask {
         clearCacheLambda()
     }