meta-gnome: drop ${PYTHON_PN}

python 2 is long unsupported, so we no longer need this variable

Signed-off-by: Tim Orling <tim.orling@konsulko.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-gnome/recipes-gnome/gnome-shell/gnome-shell_45.4.bb

@@ -50,7 +50,7 @@ EXTRA_OEMESON = " \
 do_install:append() {
     # fix shebangs
     for tool in `find ${D}${bindir} -name '*-tool'`; do
-        sed -i 's:#!${PYTHON}:#!${bindir}/${PYTHON_PN}:' $tool
+        sed -i 's:#!${PYTHON}:#!${bindir}/python3:' $tool
     done
 }