refactor: remove parallel runs

Makefile

diff --git a/Makefile b/Makefile
index f319f4c..087d172 100644
--- a/Makefile
+++ b/Makefile
@@ -318,9 +318,9 @@
 	
 .PHONY: caravel-sta
 caravel-sta: ./env/spef-mapping.tcl
-	@$(MAKE) -C $(TIMING_ROOT) -f $(TIMING_ROOT)/timing.mk caravel-timing-typ -j3
-	@$(MAKE) -C $(TIMING_ROOT) -f $(TIMING_ROOT)/timing.mk caravel-timing-fast -j3
-	@$(MAKE) -C $(TIMING_ROOT) -f $(TIMING_ROOT)/timing.mk caravel-timing-slow -j3
+	@$(MAKE) -C $(TIMING_ROOT) -f $(TIMING_ROOT)/timing.mk caravel-timing-typ
+	@$(MAKE) -C $(TIMING_ROOT) -f $(TIMING_ROOT)/timing.mk caravel-timing-fast
+	@$(MAKE) -C $(TIMING_ROOT) -f $(TIMING_ROOT)/timing.mk caravel-timing-slow
 	@echo =================================================Summary=================================================
 	@find $(PROJECT_ROOT)/signoff/caravel/openlane-signoff -name "*-summary.rpt" | head -n1 \
 		| xargs tail -n2 | head -n1