Use pom-less plugins where we can

Use pom-less plugins where we can

Tycho 0.24 introduced pom-less builds [1]. With this, we can
remove the pom.xml in any plugin, test or feature plugin that
uses the default configuration.

This bumps the minimum required version of Maven to 3.3.

Some plugins have extra specific configuration in their pom,
like ctf or pcap traces that call maven-antrun-plugin to
download test traces. These will still need their usual pom.xml
file.

For test plugins, the top-level pom defines the configuration
used for *core* tests. UI and SWTBot tests use slightly
different parameters. Instead of repeating this information in
every single plugin, we can define profiles that are only
activated in those plugins.

Using empty files to selectively enable these profiles looks a
bit clunky, but it is the simplest solution I have found.
Suggestions welcome!

[1] https://wiki.eclipse.org/Tycho/Release_Notes/0.24#POM-less_Tycho_builds

Change-Id: Ibd379905ca52cd1535b8f5a92e58e1f1fb311a19
Signed-off-by: Alexandre Montplaisir <alexmonthy@efficios.com>
Reviewed-on: https://git.eclipse.org/r/63050
Reviewed-by: Hudson CI