net: ibm: emac: remove unused sysrq handler for 'c' key

Since commit d6580a9f ("kexec: sysrq: simplify sysrq-c handler"),
the sysrq handler for the 'c' key has been sysrq_crash_op.  Debugging
code in the ibm_emac driver also tries to register a handler for the 'c'
key, but this has no effect because register_sysrq_key() doesn't replace
existing handlers.  Since evidently no one has cared enough to fix this
in the last 8 years, and it's very rare for drivers to register sysrq
handlers (for good reason), just remove the dead code.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>