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-pyparsing_3.1.1.bb

@@ -17,14 +17,14 @@ UPSTREAM_CHECK_REGEX = "pyparsing-(?P<pver>.*)\.tar"
 inherit pypi python_flit_core
 
 RDEPENDS:${PN} += " \
-    ${PYTHON_PN}-datetime \
-    ${PYTHON_PN}-debugger \
-    ${PYTHON_PN}-html \
-    ${PYTHON_PN}-json \
-    ${PYTHON_PN}-netclient \
-    ${PYTHON_PN}-pprint \
-    ${PYTHON_PN}-stringold \
-    ${PYTHON_PN}-threading \
+    python3-datetime \
+    python3-debugger \
+    python3-html \
+    python3-json \
+    python3-netclient \
+    python3-pprint \
+    python3-stringold \
+    python3-threading \
 "
 
 BBCLASSEXTEND = "native nativesdk"