Update git submodules

* Update docs/submodules/yardstick from branch 'stable/euphrates'
  - Remove checkno.png and checkyes.png due to license issue

    JIRA: YARDSTICK-817

    Since checkno.png and checkyes.png is not Apache-2 license based.
    so we need to remove them.

    Change-Id: I40dd303fb54a3736ca969ac1c186d2cd23408436
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>
    (cherry picked from commit da0163b7b7aaf3ede4e757a0b7d94a5ea99b1083)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 8505931..7e0574b 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 850593125ca388b7157f2a8e1966e05a1caa0ab1
+Subproject commit 7e0574b0ef0c8aa7c52865f4d80f96018bd5821b