chore(deps): Drop swiftmailer/swiftmailer

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

diff --git a/3rdparty b/3rdparty
index 6f18457f7dfcf23ce2877495a9323a144fd4a166..b28af7ccf0bebff554672543fbbfe0e5d99968bd 160000 (submodule)
--- a/3rdparty
+++ b/3rdparty
@@ -1 +1 @@
-Subproject commit 6f18457f7dfcf23ce2877495a9323a144fd4a166
+Subproject commit b28af7ccf0bebff554672543fbbfe0e5d99968bd