Remove -sha256 flag when calling bssl_inject_hash.

Cherry-pick note: Needed for the BoringSSL change in the same topic due to build flag changes.

Flag removed upstream, all platforms now use SHA-256
for libcrypto integrity hash.

Test: m && flashall
Change-Id: I453edebb80ec2a853d54ce5c3f055b6456010524
(cherry picked from commit c0d89b3d)
Merged-In: I453edebb80ec2a853d54ce5c3f055b6456010524