Cleanup build.properties

Remove "javacDefaultEncoding.."
- The default encoding of source files is defined in parent pom by
  project.build.sourceEncoding.
- Since all our Java code is UTF-8, it's sufficient to set it globally.

Remove javacSource, javacTarget, jre.compilation.profile
- The compiler level is derived from the BREE header in MANIFEST.MF
  files, if not overridden by a pom file or build.properties. For the
  precedence, see https://bugs.eclipse.org/bugs/show_bug.cgi?id=353505.
- There is no good reason for us to override the compiler level derived
  from the BREE in the build, so let's avoid the duplication in the
  build.properties.