Remove helper from Makefile

Signed-off-by: Scott Wilson <scott@propersquid.com>

Author: scott-wilson

Makefile

@@ -55,10 +55,6 @@ ifneq (${NAMESPACE},)
 MY_CMAKE_FLAGS += -DOIIO_NAMESPACE:STRING=${NAMESPACE}
 endif
 
-ifneq (${BUILD_MISSING_DEPS},)
-MY_CMAKE_FLAGS += -DOpenImageIO_BUILD_MISSING_DEPS=all
-endif
-
 ifneq (${USE_PYTHON},)
 MY_CMAKE_FLAGS += -DUSE_PYTHON:BOOL=${USE_PYTHON}
 endif