Remove deprecated python3-selectors from the RDEPENDS

The python3-selectors package was removed as part of the migration to the
json manifest file.  The functionality is now part of core

Signed-off-by: Derek Straka <derek@asterius.io>
Signed-off-by: Armin Kuster <akuster808@gmail.com>

meta-python/recipes-devtools/python/python3-pyserial_3.4.bb

@@ -5,5 +5,3 @@ do_install_append() {
     rm -f ${D}${bindir}/miniterm.py
     rmdir ${D}${bindir}
 }
-
-RDEPENDS_${PN} += "${PYTHON_PN}-selectors"