Revert "fix: Add getClass() to FieldColour. (#2506)"

This reverts commit f5a577b.

Author: gonfunko

plugins/field-colour/src/field_colour.ts

@@ -728,15 +728,6 @@ export class FieldColour extends Blockly.Field<string> {
     // the static fromJson method.
     return new this(options.colour, undefined, options);
   }
-
-  /**
-   * Returns the class of this field.
-   *
-   * @returns FieldColour.
-   */
-  getClass() {
-    return FieldColour;
-  }
 }
 
 /** The default value for this field. */