tests: Remove ext4 option from rados:thrash tests

Signed-off-by: Vasu Kulkarni <vasu@redhat.com>
(manual cherry-pick from ceph-qa-suite 1fcc4457144278f77dd8462ecf34948a11dcb2a9)

diff --git a/qa/suites/rados/thrash/fs/ext4.yaml b/qa/suites/rados/thrash/fs/ext4.yaml
deleted file mode 120000 (symlink)
index 65d7188..0000000
--- a/qa/suites/rados/thrash/fs/ext4.yaml
+++ /dev/null
@@ -1 +0,0 @@
-../../../../fs/ext4.yaml
\ No newline at end of file