libc: Remove non-Arm files

Remove all files that don't have only Arm copyright. This is the first
step to cleanup the C library in this repository. They will be re-added
in the following patches.

Change-Id: I72c40a1620d1df3228fc397ec695d569a20245fd
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>