Remove cliff-tablib from requirements.txt

No longer needed

Change-Id: I07c72fd34e9a7429d6fb910e254f91e888070009

Author: Dean Troyer

requirements.txt

@@ -6,7 +6,6 @@ six>=1.9.0
 
 Babel>=1.3
 cliff>=1.14.0 # Apache-2.0
-cliff-tablib>=1.0
 os-client-config!=1.6.2,>=1.4.0
 oslo.config>=2.3.0 # Apache-2.0
 oslo.i18n>=1.5.0 # Apache-2.0