Get rid of the libqemustub.a remainders

libqemustub.a has been removed in commit ebedb37c8d ("Makefile: Remove
libqemustub.a"). Some remainders have been missed. Remove them now.

Message-Id: <20200804170055.2851-8-thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>

scripts/coverity-scan/run-coverity-scan

@@ -403,9 +403,6 @@ echo "Configuring..."
     --enable-mpath --enable-libxml2 --enable-glusterfs \
     --enable-virtfs --enable-zstd
 
-echo "Making libqemustub.a..."
-make libqemustub.a
-
 echo "Running cov-build..."
 rm -rf cov-int
 mkdir cov-int