mbedtls: remove support for mbedtls 2.x

Signed-off-by: Lauren Wehrmeister <lauren.wehrmeister@arm.com>
Change-Id: I57837fcce4e4c3159d16fbe34771868281bbe939
(cherry picked from commit 32eb4a6eabe2c74710fef6c35d898e37cfe77c96)
5 files changed