make the weak XML_SetHashSalt16Bytes reference in pyexpat
unversioned (.symver): linked against the tuxcare libexpat it was stamped
with the EXPAT_2_0_1_RH version node, and on el6 glibc 2.12 a versioned
reference whose provider lacks the symbol is a fatal relocation error even
for a weak symbol, so pyexpat.so failed to load (breaking yum with
"ImportError: No module named cElementTree") on hosts whose
/lib64/libexpat.so.1 predates the els10 backport, e.g. a third-party
expat package
drop the runtime Requires on expat >= 2.0.1-13.el6_8.tuxcare.els10:
a third-party package providing a higher expat NEVRA satisfies it without
providing the ABI, and with the truly-weak unversioned reference pyexpat
degrades gracefully to XML_SetHashSalt when the symbol is absent