Remove definition of owners-common as a plugin

The owners-common module of the owners' plugin isn't a plugin itself but
simply a Java library definition of classes shared between owners and
owners-autoassign.

Remove the plugin definition of owners-common and resume the correct
build of the module.

Change-Id: I05e7d96f66bccbdfc67bf26c65437edbe73d3906

owners-common/BUILD

diff --git a/owners-common/BUILD b/owners-common/BUILD
index cf10c1e..faf2d08 100644
--- a/owners-common/BUILD
+++ b/owners-common/BUILD
@@ -11,12 +11,6 @@
     deps = PLUGIN_DEPS_NEVERLINK + EXTERNAL_DEPS,
 )
 
-gerrit_plugin(
-    name = "owners-common__plugin",
-    srcs = glob(["src/main/java/**/*.java"]),
-    resources = glob(["src/main/resources/**/*"]),
-)
-
 junit_tests(
     name = "test",
     testonly = 1,