Drop support for TEST_REPORTS

We always use the text report on the UART so drop the other report
formats (Junit) and destinations (file over semihosting). This
simplifies the report generation code.

Change-Id: I64e105d8c773e31d63a4ed06999d24f946a40014
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>