refactor(build): Merge all plugins

Otherwise rebar runs in a dead-loop

rebar.config

@@ -1,6 +1,7 @@
 {minimum_otp_vsn, "21.3"}.
-{plugins,[{relup_helper,{git,"https://github.com/emqx/relup_helper",
-                             {branch,"master"}}}]}.
+{plugins,[ {relup_helper,{git,"https://github.com/emqx/relup_helper", {branch,"master"}}}
+         , {coveralls, {git, "https://github.com/emqx/coveralls-erl", {branch, "github"}}}
+         ]}.
 {edge_relx_overlay,[]}.
 {edoc_opts,[{preprocess,true}]}.
 {erl_opts,[warn_unused_vars,warn_shadow_vars,warn_unused_import,
@@ -51,13 +52,7 @@
                {overlay, ["${BASIC_OVERLAYS}", "${EDGE_OVERLAYS}"]},
                {overlay_vars,["vars/vars-edge.config","vars/vars-pkg.config"]}]}]},
      {test,
-        [
-          {plugins, [
-            rebar3_proper,
-            {coveralls,
-              {git, "https://github.com/emqx/coveralls-erl",
-                {branch, "github"}}}]},
-          {deps,
+        [{deps,
           [ {bbmustache, "1.7.0"},
             {emqtt, {git, "https://github.com/emqx/emqtt", {tag, "1.2.0"}}},
             {emqx_ct_helpers, {git, "https://github.com/emqx/emqx-ct-helpers", {tag, "1.3.0"}}},