hob-toolchain: Update for removal of dummy classes

Without this hob will fail to parse.

(From OE-Core rev: b63ba9104584c5aa15792fcfe706d59d39235ad0)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-hob/recipes-core/meta/hob-toolchain.bb

@@ -6,5 +6,4 @@ PR = "r0"
 LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=3f40d7994397109285ec7b81fdeb3b58 \
                     file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
 
-IMAGETEST ?= "dummy"
-inherit populate_sdk imagetest-${IMAGETEST}
+inherit populate_sdk