INSTALL, RELEASE, cmd.mk, lint-man.mk: Use expr(1) instead of bc(1)

INSTALL, RELEASE, cmd.mk, lint-man.mk: Use expr(1) instead of bc(1)

Both bc(1) and expr(1) are in POSIX.  However, expr(1) is provided by
GNU coreutils, and seems simpler to use.  This will simplify the
dependencies required to package the project.

Document the change in dependencies too.

Signed-off-by: Alejandro Colomar <alx@kernel.org>