python-packages: Clean up build variables

* Rename PYTHON3_PKG_SETUP_VARS to PYTHON3_PKG_BUILD_VARS, and
  PYTHON3_PKG_SETUP_DIR to PYTHON3_PKG_BUILD_PATH

  The new variable names emphasize that these values apply to the new
  build process.

* Remove PYTHON3_PKG_SETUP_ARGS set to the empty string

  These were set to override the default arguments in the old build
  process and not applicable to the new build process.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

lang/python/python-docker/Makefile

@@ -2,7 +2,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=python-docker
 PKG_VERSION:=6.0.1
-PKG_RELEASE:=2
+PKG_RELEASE:=3
 
 PYPI_NAME:=docker
 PKG_HASH:=896c4282e5c7af5c45e8b683b0b0c33932974fe6e50fc6906a0a83616ab3da97
@@ -17,8 +17,6 @@ include ../pypi.mk
 include $(INCLUDE_DIR)/package.mk
 include ../python3-package.mk
 
-PYTHON3_PKG_SETUP_ARGS:=
-
 define Package/python3-docker
   SECTION:=lang
   CATEGORY:=Languages