HPCC-9892 Remove need for LOADXML for template language

Code to do this was already implemented however, it was still being reported as an error
and thus finally aborting compilation. Also removed dummy uses of LOADXML within ecl/regress/ and testing/ecl/regress/.

deletions of:
LOADXML('<xml/>')
LOADXML('<xml></xml>')
LOADXML('<xml>dummy</xml>')

Signed-off-by: jamienoss <james.noss@lexisnexis.com>