package/python3: drop unrecognized option

--enable-old-stdlib-cache is not recognozed since at least version
3.6.3, see:
http://autobuild.buildroot.org/results/b957f956100fc36c7d5ffab1d7df41a65ae52ded

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/python3/python3.mk

@@ -70,10 +70,6 @@ else
 PYTHON3_CONF_OPTS += --with-expat=none
 endif
 
-ifeq ($(BR2_PACKAGE_PYTHON3_PYC_ONLY),y)
-PYTHON3_CONF_OPTS += --enable-old-stdlib-cache
-endif
-
 ifeq ($(BR2_PACKAGE_PYTHON3_SQLITE),y)
 PYTHON3_DEPENDENCIES += sqlite
 else