Remove requirement on oslo.serialization
This is unused.
@@ -7,7 +7,6 @@ Babel!=2.4.0,>=2.3.4 # BSD
eventlet!=0.18.3,!=0.20.1,<0.21.0,>=0.18.2 # MIT
oslo.concurrency>=3.20.0 # Apache-2.0
oslo.log>=3.30.0 # Apache-2.0
-oslo.serialization!=2.19.1,>=2.18.0 # Apache-2.0
oslo.i18n>=3.15.3 # Apache-2.0
oslo.privsep>=1.23.0 # Apache-2.0
oslo.service!=1.28.1,>=1.24.0 # Apache-2.0
