Bug#912392: scilab FTBFS with OpenJDK 11

[Emmanuel Bourg]

The @Generated annotations can be safely removed, they only have a
documentation purpose at the source level.

But after removing them there is another issue related to the removal
of the javax.activation API in Java 11:

    [javac] /build/scilab-6.0.1/modules/helptools/src/java/org/scilab/modules/helptools/image/ImageConverter.java:33: error: package javax.activation does not exist
    [javac] import javax.activation.MimetypesFileTypeMap;
    [javac]                        ^
    [javac] /build/scilab-6.0.1/modules/helptools/src/java/org/scilab/modules/helptools/image/ImageConverter.java:50: error: cannot find symbol
    [javac]     private MimetypesFileTypeMap mimeMap = new MimetypesFileTypeMap();
    [javac]             ^
    [javac]   symbol:   class MimetypesFileTypeMap
    [javac]   location: class ImageConverter
    [javac] 2 errors
    [javac] 3 warnings