refactor(build): Delete _checkouts

The `_checkouts` directory was handy when we had to git clone
rebar dependencies in a release project and make changes inside

Now since this is an umbrella project, there is no reason to keep it

packages.mk

@@ -32,7 +32,7 @@ endif
 .PHONY: $(PROFILES:%=relup-%)
 $(PROFILES:%=relup-%): $(REBAR)
 ifneq ($(OS),Windows_NT)
-	@ln -snf _build/$(@:relup-%=%)/lib ./_checkouts
+	@ln -snf _build/$(@:relup-%=%)/lib
 	@if [ ! -z $$(ls | grep -E "$(@:relup-%=%)-$(SYSTEM)-(.*)-$$(uname -m).zip" | head -1 ) ]; then \
 		mkdir -p tmp/relup_packages/$(@:relup-%=%); \
 		cp $(@:relup-%=%)-$(SYSTEM)-*-$$(uname -m).zip tmp/relup_packages/$(@:relup-%=%); \
@@ -43,7 +43,7 @@ endif
 .PHONY: $(PROFILES:%=%-tar) $(PKG_PROFILES:%=%-tar)
 $(PROFILES:%=%-tar) $(PKG_PROFILES:%=%-tar): $(REBAR)
 ifneq ($(OS),Windows_NT)
-	@ln -snf _build/$(subst -tar,,$(@))/lib ./_checkouts
+	@ln -snf _build/$(subst -tar,,$(@))/lib
 endif
 ifneq ($(shell echo $(@) |grep edge),)
 	export EMQX_DESC="EMQ X Edge"

rebar.config

@@ -159,11 +159,11 @@
     , {template, "data/loaded_plugins.tmpl", "data/loaded_plugins"}
     , {template, "data/loaded_modules.tmpl", "data/loaded_modules"}
     , {template,"data/emqx_vars","releases/emqx_vars"}
-    , {copy,"_checkouts/cuttlefish/cuttlefish","bin/"}
+    , {copy,"_build/default/lib/cuttlefish/cuttlefish","bin/"}
     , {copy,"bin/*","bin/"}
     , {template,"etc/*.conf","etc/"}
     , {template,"etc/emqx.d/*.conf","etc/emqx.d/"}
-    , {copy,"_checkouts/emqx/priv/emqx.schema","releases/{{rel_vsn}}/"}
+    , {copy,"priv/emqx.schema","releases/{{rel_vsn}}/"}
     , {copy, "etc/certs","etc/"}
     , "${RELUP_OVERLAYS}"
     ]
@@ -176,7 +176,7 @@
     , {copy,"bin/emqx_ctl","bin/emqx_ctl-{{rel_vsn}}"}
     , {copy,"bin/install_upgrade.escript", "bin/install_upgrade.escript-{{rel_vsn}}"}
     , {copy,"bin/nodetool","bin/nodetool-{{rel_vsn}}"}
-    , {copy,"_checkouts/cuttlefish/cuttlefish","bin/cuttlefish-{{rel_vsn}}"}
+    , {copy,"_build/default/lib/cuttlefish/cuttlefish","bin/cuttlefish-{{rel_vsn}}"}
     ]
   },