Revert "Added `sbt-legacy` profile for building IDE to accomodate

https://github.com/scala-ide/scala-ide/pull/472"

This reverts commit ed56efa9123f216fe050b1f284dd85fef7e0a3e7.

The maven `sbt-new` profile that was introduced by SHA:
fa2740d6c9c35196169466c285c0d51257f36488 no longer needs to be passed because,
as of now, that is the default working mode of the Scala IDE build
(https://github.com/scala-ide/scala-ide/pull/548).