run-ci: ensure old generated content is removed

Remove the old generated directories before re-running the generate
script in order to detect if spurious files are left in place.

See I9dcc51fd23f2dac56b7b8efca57ca789e3075309 as an example of spurious
files previously being identified.

Tested: Pushed this change to Gerrit in front of I9dcc51f and confirmed
        the CI failure that is fixed by that commit.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ia27fbe11f8ef6399da05bbeb741e818e77d859cf
diff --git a/gen/run-ci b/gen/run-ci
index d38927a..49c9544 100755
--- a/gen/run-ci
+++ b/gen/run-ci
@@ -1,5 +1,6 @@
 #!/bin/bash
 cd "$(dirname "$0")" || exit
+find . -mindepth 1 -maxdepth 1 -type d -exec rm -r {} \;
 ./regenerate-meson || exit
 rc=0
 git --no-pager diff --exit-code -- . || rc=$?