Remove FIRRTL_LOGLEVEL dead make variable

variables.mk

@@ -9,7 +9,6 @@ HELP_COMPILATION_VARIABLES = \
 "   SBT_OPTS          = set additional sbt command line options (these take the form -Dsbt.<option>=<setting>) " \
 "                       See https://www.scala-sbt.org/1.x/docs/Command-Line-Reference.html\#Command+Line+Options" \
 "   SBT               = if overridden, used to invoke sbt (default is to invoke sbt by sbt-launch.jar)" \
-"   FIRRTL_LOGLEVEL   = if overridden, set firrtl log level (default is error)"
 
 HELP_PROJECT_VARIABLES = \
 "   SUB_PROJECT            = use the specific subproject default variables [$(SUB_PROJECT)]" \
@@ -258,8 +257,6 @@ define run_sbt_assembly
 	cd $(base_dir) && $(SBT) ";project $(1); set assembly / assemblyOutputPath := file(\"$(2)\"); assembly" && touch $(2)
 endef
 
-FIRRTL_LOGLEVEL ?= error
-
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 # output directory for tests
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