ion: remove ion_share_set_flags

Due to changes in the semantics of the `flags' field of `struct
ion_buffer', it is no longer necessary to set the flags when setting
up an ion share.

Change-Id: I2f34868cc6d2045f78dbd5f0a67d3e40778af0de
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>