fix(location): remove base class from PlaceIndex class (#31287)

### Issue # (if applicable)

None

### Reason for this change
I implemented the location resources in #30711 and #30682. 

During the review, it was suggested that it would be better not to have a base class.
As a result, the `GeofenceCollection` class and `RouteCalculator` class do not have a base class. 

#30711 (comment)

On the other hand, the `PlaceIndex `class has already been implemented with a base class, which is inconsistent with the current approach.



### Description of changes
Remove a unnecessary base class from `PlaceIndex` class.



### Description of how you validated changes
Re-run unit tests and integ tests.


### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-location-alpha/lib/place-index.ts

@@ -74,39 +74,12 @@ export enum IntendedUse {
   STORAGE = 'Storage',
 }
 
-abstract class PlaceIndexBase extends Resource implements IPlaceIndex {
-  public abstract readonly placeIndexName: string;
-  public abstract readonly placeIndexArn: string;
-
-  /**
-   * Grant the given principal identity permissions to perform the actions on this place index.
-   */
-  public grant(grantee: iam.IGrantable, ...actions: string[]): iam.Grant {
-    return iam.Grant.addToPrincipal({
-      grantee: grantee,
-      actions: actions,
-      resourceArns: [this.placeIndexArn],
-    });
-  }
-
-  /**
-   * Grant the given identity permissions to search using this index
-   */
-  public grantSearch(grantee: iam.IGrantable): iam.Grant {
-    return this.grant(grantee,
-      'geo:SearchPlaceIndexForPosition',
-      'geo:SearchPlaceIndexForSuggestions',
-      'geo:SearchPlaceIndexForText',
-    );
-  }
-}
-
 /**
  * A Place Index
  *
  * @see https://docs.aws.amazon.com/location/latest/developerguide/places-concepts.html
  */
-export class PlaceIndex extends PlaceIndexBase {
+export class PlaceIndex extends Resource implements IPlaceIndex {
   /**
    * Use an existing place index by name
    */
@@ -130,7 +103,7 @@ export class PlaceIndex extends PlaceIndexBase {
       throw new Error(`Place Index Arn ${placeIndexArn} does not have a resource name.`);
     }
 
-    class Import extends PlaceIndexBase {
+    class Import extends Resource implements IPlaceIndex {
       public readonly placeIndexName = parsedArn.resourceName!;
       public readonly placeIndexArn = placeIndexArn;
     }
@@ -187,4 +160,25 @@ export class PlaceIndex extends PlaceIndexBase {
     this.placeIndexUpdateTime = placeIndex.attrUpdateTime;
   }
 
+  /**
+   * Grant the given principal identity permissions to perform the actions on this place index.
+   */
+  public grant(grantee: iam.IGrantable, ...actions: string[]): iam.Grant {
+    return iam.Grant.addToPrincipal({
+      grantee: grantee,
+      actions: actions,
+      resourceArns: [this.placeIndexArn],
+    });
+  }
+
+  /**
+   * Grant the given identity permissions to search using this index
+   */
+  public grantSearch(grantee: iam.IGrantable): iam.Grant {
+    return this.grant(grantee,
+      'geo:SearchPlaceIndexForPosition',
+      'geo:SearchPlaceIndexForSuggestions',
+      'geo:SearchPlaceIndexForText',
+    );
+  }
 }