toolchain-external: remove SOURCE/SITE for locally available toolchain

When the custom external toolchain is locally available, we currently
define SITE/SOURCE to empty variables. Now that the package
infrastructure doesn't define a value for SOURCE when VERSION is empty,
it doesn't attempt to download a file anymore, so we can get rid of
those empty SOURCE/SITE variables in the toolchain-external package.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

toolchain/toolchain-external/toolchain-external.mk

@@ -453,14 +453,6 @@ TOOLCHAIN_EXTERNAL_ACTUAL_SOURCE_TARBALL ?= \
 	$(subst -i686-pc-linux-gnu.tar.bz2,.src.tar.bz2,$(subst -i686-pc-linux-gnu-i386-linux.tar.bz2,-i686-pc-linux-gnu.src.tar.bz2,$(TOOLCHAIN_EXTERNAL_SOURCE)))
 endif
 
-# In fact, we don't need to download the toolchain, since it is already
-# available on the system, so force the site and source to be empty so
-# that nothing will be downloaded/extracted.
-ifeq ($(BR2_TOOLCHAIN_EXTERNAL_PREINSTALLED),y)
-TOOLCHAIN_EXTERNAL_SITE =
-TOOLCHAIN_EXTERNAL_SOURCE =
-endif
-
 TOOLCHAIN_EXTERNAL_ADD_TOOLCHAIN_DEPENDENCY = NO
 
 TOOLCHAIN_EXTERNAL_INSTALL_STAGING = YES