lang/python: restore USES=python variables and SUB_LIST (no-op)

Has been a to do item for time. These are independent from but used
by the bytecode trigger.

lang/python39/Makefile

@@ -15,8 +15,8 @@ LICENSE=	PSFL
 
 LIB_DEPENDS=	libffi.so:devel/libffi
 
-USES=		compiler:c11 cpe ncurses pathfix pkgconfig readline \
-		shebangfix ssl tar:xz
+USES=		compiler:c11 cpe ncurses pathfix pkgconfig \
+		python:${PYTHON_DISTVERSION:R},env readline shebangfix ssl tar:xz
 PATHFIX_MAKEFILEIN=	Makefile.pre.in
 USE_LDCONFIG=	yes
 GNU_CONFIGURE=	yes
@@ -26,11 +26,6 @@ SHEBANG_FILES+=	Lib/test/ziptestdata/exe_with_z64 \
 		Lib/test/ziptestdata/exe_with_zip \
 		Lib/test/ziptestdata/header.sh
 
-# Duplicate python.mk variables. TODO: Let lang/python?? ports use python.mk bits.
-PYTHON_VER=		${PYTHON_DISTVERSION:R}
-PYTHON_VERSION=		python${PYTHON_VER}
-PYTHON_SUFFIX=		${PYTHON_VER:S/.//g}
-
 DISABLED_EXTENSIONS=	_sqlite3 _tkinter _gdbm
 CONFIGURE_ARGS+=	--enable-shared --without-ensurepip \
 			--with-system-ffi