Revert "lib/sha1.c: quiet sparse noise about symbol not declared"

This reverts commit 1a432549252080202083b91c573b79c4a678b4e6.
Revert "Remove ARM sha1 routines"

This reverts commit 182963726b13e2eca81cada95f1291f154d3ca30.
Revert "lib/sha1: use the git implementation of SHA-1"

This reverts commit b4bd1549591c132e5428a7c270954d34d63cdd37.