run-build.sh: Remove superfluous handling in case BUILD_TARGET is set

After recent refactor of splitting build command to seperate sub-commands,
we don't need to do adhoc parsing with "head" like before. So, remove to
avoid confusion.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: Ib4c66c384d5aaa6f30edec50776f031ab87cd65c
diff --git a/run-build.sh b/run-build.sh
index 1c92425..9377b3f 100755
--- a/run-build.sh
+++ b/run-build.sh
@@ -63,7 +63,6 @@
 eval $set_compiler_cmd
 
 if [ -n "$BUILD_TARGET" ]; then
-    cmake_build_cmd=$(echo "$cmake_build_cmd" | head -4)
     cmake_build_cmd=${cmake_build_cmd/-- install/-- $BUILD_TARGET}
 fi