remoteproc: Drop dangling find_rsc_table dummies

As the core now deals with the lack of a resource table, remove the
dangling custom dummy implementations of find_rsc_table from drivers.

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>