Remove gmock from sdk as it is part of gtest 1.8

From googlttest 1.8, gmock becomes part of gtest, and its recipe is
dropped from upstream.
Remove it from SDK, gtest will provide both gtest and gmock libraries.

Change-Id: Iea14e81bda08e97dbeb9eddee8991f22cb8478be
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/common/recipes-core/packagegroups/packagegroup-core-standalone-sdk-target.bbappend b/common/recipes-core/packagegroups/packagegroup-core-standalone-sdk-target.bbappend
index ebfb91a..7eef4f9 100644
--- a/common/recipes-core/packagegroups/packagegroup-core-standalone-sdk-target.bbappend
+++ b/common/recipes-core/packagegroups/packagegroup-core-standalone-sdk-target.bbappend
@@ -1 +1 @@
-RRECOMMENDS_${PN}_append = " gtest gmock sdbusplus phosphor-logging libstdc++-staticdev"
+RRECOMMENDS_${PN}_append = " gtest sdbusplus phosphor-logging libstdc++-staticdev"