python: Drop ${PYTHON_PN}

python 2 is gone and we don't need the abstraction now, drop the remaining usage
of this variable.

The definition in python3-dir.bbclass is left for now for other layers.

(From OE-Core rev: b566b1e32c7993d1ab7795562f648e52ce186a70)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/python/python3-atomicwrites_1.4.1.bb

@@ -12,9 +12,9 @@ SRC_URI += " \
 "
 
 RDEPENDS:${PN}-ptest += " \
-	${PYTHON_PN}-pytest \
-	${PYTHON_PN}-unittest-automake-output \
-	${PYTHON_PN}-unixadmin \
+	python3-pytest \
+	python3-unittest-automake-output \
+	python3-unixadmin \
 "
 
 do_install_ptest() {
@@ -22,6 +22,6 @@ do_install_ptest() {
 	cp -rf ${S}/tests/* ${D}${PTEST_PATH}/tests/
 }
 
-RDEPENDS:${PN} = "${PYTHON_PN}-misc"
+RDEPENDS:${PN} = "python3-misc"
 
 BBCLASSEXTEND = "native nativesdk"