Revert upstream default to GTK2

Revert upstream default to GTK2

OpenJDK 11 uses GTK3 by default for the GTK Look and Feel but it still
has too many pending issues and artifacts and is not on par with GTK2
support. This patch is the reverse of the upstream commit which ensures
that GTK2 is tried before GTK3.
 When GTK3 becomes better supported we should drop this and update the
 dlopen_jre_depends variable in debian/rules accordingly.
Origin: upstream, http://hg.openjdk.java.net/jdk-updates/jdk11u/rev/3e3696a308e1
Bug: https://bugs.openjdk.java.net/browse/JDK-8198649,
     https://bugs.java.com/bugdatabase/view_bug.do?bug_id=JDK-8198654
Bug-Ubuntu: https://launchpad.net/bugs/1770278
Forwarded: not-needed
Applied-Upstream: http//hg.openjdk.java.net/jdk-updates/jdk11u/rev/3e3696a308e1
Reviewed-by: <name and email of a reviewer, optional>
Last-Update: 2019-03-27 <YYYY-MM-DD, last update of the meta-information, optional>

Gbp-Pq: Name keep-gtk2-as-default.patch