Revert "Change scope of vaadin-core to prevent conflicts"

This reverts commit 39f6228.

This is not working as the Vaadin Maven Plugin otherwise throws errors during prepare-frontend like:
``Failed to execute goal com.vaadin:vaadin-maven-plugin:24.5.3:prepare-frontend (default) on project vaadin-simple-grid-filter: Could not execute prepare-frontend goal. Error occured during goal execution: Cannot invoke "java.lang.Class.isInterface()" because the return value of "org.reflections.Reflections.forClass(String, java.lang.ClassLoader[])" is null``

Fixes xdev-software/vaadin-simple-grid-filter#20

Author: AB-xdev

template-placeholder/pom.xml

@@ -103,8 +103,6 @@
 		<dependency>
 			<groupId>com.vaadin</groupId>
 			<artifactId>vaadin-core</artifactId>
-			<!-- "provided" to prevent conflicts in final project. It's assumed that Vaadin is already present -->
-			<scope>provided</scope>
 		</dependency>
 	</dependencies>