Setting the default LINK_TARGETS to none

- The installation can run in docker containers by default of course at the cost
  of disk space.

sky130/Makefile

diff --git a/sky130/Makefile b/sky130/Makefile
index b58e768..5c6a060 100644
--- a/sky130/Makefile
+++ b/sky130/Makefile
@@ -72,9 +72,8 @@
 # from source, where they don't.
 
 # LINK_TARGETS = source
-# LINK_TARGETS = none
+LINK_TARGETS = none
 # LINK_TARGETS = sky130A
-LINK_TARGETS = source
 
 # Paths: