trace-cmd: Remove unused variable LD_SO_CONF_DIR

The LD_SO_CONF_DIR variable in the Makefile is not used anywhere. Remove it.

Link: https://lore.kernel.org/linux-trace-devel/20201216044213.357761288@goodmis.org

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
diff --git a/Makefile b/Makefile
index f8252ba..e956a2e 100644
--- a/Makefile
+++ b/Makefile
@@ -114,7 +114,6 @@
 #' emacs highlighting gets confused by the above escaped quote.
 
 BASH_COMPLETE_DIR ?= $(etcdir)/bash_completion.d
-LD_SO_CONF_DIR ?= $(etcdir)/ld.so.conf.d
 
 export PLUGIN_DIR_TRACEEVENT
 export PLUGIN_DIR_TRACECMD