remoteproc: Remove depricated crash completion

The crash handling now happens in a single execution context, so there's
no longer a need for a completion to synchronize this.

Reviewed-By: Loic Pallardy <loic.pallardy@st.com>
Tested-By: Loic Pallardy <loic.pallardy@st.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>