Remove now unnecessary suppression of warning about missing serial-UID

See
- eclipse-jdt/eclipse.jdt.core#4210 (comment)

Author: HannesWell

org.eclipse.jdt.launching/launching/org/eclipse/jdt/internal/launching/sourcelookup/advanced/FileHashing.java

@@ -128,7 +128,6 @@ private static class HasherImpl implements Hasher {
 
 		private final Map<CacheKey, HashCode> cache;
 
-		@SuppressWarnings("serial")
 		public HasherImpl(int cacheSize) {
 			this.cache = new LinkedHashMap<>() {
 				@Override