Fix unit test for goext (#938)

Why I did it
#937
PR checker is blocked by goext build

How I did it
Remove go build, and keep go test to run unit test.

How to verify it
Pass all UT and E2E test cases.

goext/Makefile

@@ -17,7 +17,6 @@ all:
 	$(SWIG) $(SWIG_FLAG) -I/usr/include/swss/ swsscommon.i
 
 check:
-	sudo CGO_LDFLAGS="$(CGO_LDFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" $(GO) build
 	sudo CGO_LDFLAGS="$(CGO_LDFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" $(GO) test
 
 clean: