Clean up non-standard use of /// comments in JavaFX

JDK-8298405 added markdown support to javadoc, using `///` to indicate markdown documentation comments. As a result, building JavaFX docs with JDK 23 produces new warnings, which causes the build to fail (since we treat warnings as errors).

$ export JDK_HOME=/path/to/jdk-23
$ gradle javadoc
...
jfx/modules/javafx.graphics/src/main/java/javafx/print/JobSettings.java:503: warning: Duplicate comment for property.
    public final StringProperty outputFileProperty() {
                                ^
  Remove the comment on the property field or on this method to suppress this warning.
jfx/modules/javafx.graphics/src/main/java/javafx/print/JobSettings.java:559: warning: Duplicate comment for property.
    public final IntegerProperty copiesProperty() {
                                 ^
  Remove the comment on the property field or on this method to suppress this warning.
jfx/modules/javafx.graphics/src/main/java/javafx/print/JobSettings.java:636: warning: Duplicate comment for property.
    public final ObjectProperty pageRangesProperty() {
                                ^
  Remove the comment on the property field or on this method to suppress this warning.
jfx/modules/javafx.graphics/src/main/java/javafx/print/JobSettings.java:820: warning: Duplicate comment for property.
    public final ObjectProperty<Collation> collationProperty() {
                                           ^
  Remove the comment on the property field or on this method to suppress this warning.
jfx/modules/javafx.graphics/src/main/java/javafx/print/JobSettings.java:1121: warning: Duplicate comment for property.
    public final ObjectProperty<PaperSource> paperSourceProperty() {
                                             ^
  Remove the comment on the property field or on this method to suppress this warning.
error: warnings found and -Werror specified
1 error
5 warnings