Remove PCE net. analyzer PceOtnNodeTest useless UT

Remove PCE net. analyzer PceOtnNodeTest useless UT

Some Junit tests in PCE network analyzer PceOtnNodeTest are pointless:
-remove these useless UT

The method isPceOtnNodeValid() in PCE network analyzer PceOtnNode was
only used by these UT. There is no need to keep it now:
- remove this method that has become useless
- remove also the method isOtnServiceTypeValid() since it was only used
  by the method isPceOtnNodeValid() now removed
- merge method isNotValid() into isValid() since apart these methods,
  it was the only other place where it was needed

JIRA: TRNSPRTPCE-572
Signed-off-by: guillaume.lambert <guillaume.lambert@orange.com>
Change-Id: Ida3653117548ad0fbfaa77a74cf1fba184878895