Rewrite aenableChart extension definition to use simple internal urls

Author: alexlipovka

input/fsh/structure-definition-enable-chart-link-id-x.fsh

@@ -2,5 +2,11 @@ Extension: EnableChart
 Id: enable-chart
 Title: "Enable Chart"
 Description: "Enable chart extension"
-* extension contains EnableChartLinkIdX named linkIdX 1..1
-* extension contains EnableChartLinkIdY named linkIdY 1..1
+* ^url = "https://emr-core.beda.software/StructureDefinition/enable-chart"
+* extension contains
+    link-id-x 1..1 and
+    link-id-y 1..1
+* extension[link-id-x].value[x] only string
+* extension[link-id-x] ^short = "Link ID for the X-axis"
+* extension[link-id-y].value[x] only string
+* extension[link-id-y] ^short = "Link ID for the Y-axis"