build: remove tracked generated .sls files and ignore them

ober

1bbdb9a7889858f22f5f66491f62f4bfe08f3f3f

diff --git a/.gitignore b/.gitignore
index 4d41fb0..ddc6dfd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -27,3 +27,4 @@ gui-snapshots.tar.gz
 # tests) can load it; the built binary registers these symbols statically.
 lib/libjerboa_native.*
 lib/libyubikey_native.*
+**/*.sls