This replaces the semantic import for the Security framework with a
classic one. Semantic imports are currently not compatible with Kotlin
Multiplatform Mobile projects which makes OLMKit (and consequently
the iOS Matrix SDK) unusable in KMM.

Fixes: https://github.com/matrix-org/olm/issues/67


Signed-off-by: Johannes Marbach <n0-0ne@mailbox.org>