Build: Remove Library Model branch in build system

Library Model is deprecated, so remove library model branch in build
system. TFM_PSA_API is defined as default and remove TFM_LIB_MODEL.

Signed-off-by: Summer Qin <summer.qin@arm.com>
Change-Id: I502f54b78d0c878356033efabed784e25284bc29
14 files changed