refactor(measured boot): remove unused extern
refactor(measured boot): remove unused extern

Change-Id: I4fb7a79c2f31973a3cd181feaface9a42bc3246f
Signed-off-by: Manish V Badarkhe <d2342ad575f6bc1a5f5a5b89d6db0f72dd7e0e4c@arm.com>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware