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-magic_0.4.27.bb

@@ -14,9 +14,9 @@ inherit pypi setuptools3
 SRC_URI[sha256sum] = "c1ba14b08e4a5f5c31a302b7721239695b2f0f058d125bd5ce1ee36b9d9d3c3b"
 
 RDEPENDS:${PN} += "file \
-                   ${PYTHON_PN}-ctypes \
-                   ${PYTHON_PN}-io \
-                   ${PYTHON_PN}-logging \
-                   ${PYTHON_PN}-shell"
+                   python3-ctypes \
+                   python3-io \
+                   python3-logging \
+                   python3-shell"
 
 BBCLASSEXTEND = "native"