holdings: remove extra titles for some fields in editor

Fixes a problem when the title of the fields
location, circulation category and electronic_location
where displayed twice in the holdings editor.

Fixes a problem when librarian can not deselect the
vendor field in the holdings editor.

* Closes rero#1452
* Closes rero#1451

Co-Authored-by: Aly Badr <aly.badr@rero.ch>

rero_ils/modules/holdings/jsonschemas/holdings/holding-v0.0.1.json

@@ -55,7 +55,6 @@
       ],
       "properties": {
         "$ref": {
-          "title": "Circulation type URI",
           "type": "string",
           "pattern": "^https://ils.rero.ch/api/item_types/.*?$",
           "form": {
@@ -74,7 +73,6 @@
       ],
       "properties": {
         "$ref": {
-          "title": "Location URI",
           "type": "string",
           "pattern": "^https://ils.rero.ch/api/locations/.+?$",
           "form": {
@@ -108,7 +106,6 @@
         "additionalProperties": false,
         "properties": {
           "uri": {
-            "title": "URI",
             "type": "string",
             "format": "uri"
           },
@@ -440,20 +437,26 @@
       ],
       "properties": {
         "$ref": {
+          "title": "Vendor URI",
           "type": "string",
           "pattern": "^https://ils.rero.ch/api/vendors/.*?$",
           "form": {
+            "focus": true,
+            "remoteOptions": {
+              "type": "vendors"
+            },
             "expressionProperties": {
               "templateOptions.required": "false"
             },
-            "remoteOptions": {
-              "type": "vendors"
+          "placeholder": "Choose a vendor",
+            "templateOptions": {
+              "label": ""
             }
           }
         }
       }
     },
-    "enumerationAndChronology": {
+      "enumerationAndChronology": {
       "title": "Available collection",
       "description": "Textual description of the basic bibliographic unit of the holding.",
       "type": "string",
@@ -581,4 +584,4 @@
       }
     }
   }
-}
+}