update api.txt

Author: BenOsodrac

core/api.txt

@@ -396,7 +396,7 @@ ion-button,prop,rel,string | undefined,undefined,false,false
 ion-button,prop,routerAnimation,((baseEl: any, opts?: any) => Animation) | undefined,undefined,false,false
 ion-button,prop,routerDirection,"back" | "forward" | "root",'forward',false,false
 ion-button,prop,shape,"rectangular" | "round" | "soft" | undefined,undefined,false,true
-ion-button,prop,size,"default" | "large" | "small" | "xlarge" | "xsmall" | undefined,undefined,false,true
+ion-button,prop,size,"default" | "large" | "small" | undefined,undefined,false,true
 ion-button,prop,strong,boolean,false,false,false
 ion-button,prop,target,string | undefined,undefined,false,false
 ion-button,prop,theme,"ios" | "md" | "ionic",undefined,false,false