[426684] Remove plugin org.eclipse.mat.tests.junit

The plugin is not needed any longer. The build & tests are running fine
without it.

Bug: 426684

Change-Id: I2dd1812175aa1dfec5aa5bf1608e2a0991d059e0
Signed-off-by: Krum Tsvetkov <krum.tsvetkov@sap.com>
8 files changed