Remove .empty file

Empty file was in place to allow committing the empty plugins directory.
This cause noise in the logs since Gerrit tries to load the .empty file as
if it was a plugin.

Removed it and left to the Makefile the creation of the directory.

Change-Id: I12741f1738e3db20bc86527c41a7bc5bd5663c7c
diff --git a/gerrit/Makefile b/gerrit/Makefile
index 7b9d7eb..6b71a07 100644
--- a/gerrit/Makefile
+++ b/gerrit/Makefile
@@ -7,6 +7,7 @@
 
 gerrit-get-plugins:
 	# Make sure Prometheus Metrics exporter plugin is installed
+	mkdir -p $(@D)/plugins
 
 	@echo "Downloading metrics-reporter-prometheus plugin $(GERRIT_BRANCH)"
 	wget $(GERRIT_CI)/plugin-metrics-reporter-prometheus-bazel-master-$(GERRIT_BRANCH)/$(LAST_BUILD)/metrics-reporter-prometheus/metrics-reporter-prometheus.jar \
diff --git a/gerrit/plugins/.empty b/gerrit/plugins/.empty
deleted file mode 100644
index e69de29..0000000
--- a/gerrit/plugins/.empty
+++ /dev/null