update {cs/cpp}/empty-block so they have the same alert message

cpp/ql/src/Best Practices/Likely Errors/EmptyBlock.ql

@@ -110,4 +110,4 @@ where
   emptyBlock(s, eb) and
   not emptyBlockContainsNonchild(eb) and
   not lineComment(eb)
-select eb, "Empty block without comment"
+select eb, "Empty block without comment."

csharp/ql/src/Likely Bugs/Statements/EmptyBlock.ql

@@ -42,4 +42,4 @@ where
   (loopStmtWithEmptyBlock(s) or conditionalWithEmptyBlock(s)) and
   not exists(CommentBlock c | c.getParent() = s) and
   not exists(ForStmt fs | fs.getBody() = s and exists(fs.getAnUpdate()))
-select s, "Empty block."
+select s, "Empty block without comment."