tpm: tpm_spapr: Remove unused tracepoint

tpm: tpm_spapr: Remove unused tracepoint

Linking of qemu-system-ppc64 fails on macOS with dtrace enabled:

  error: probe tpm_spapr_show_buffer doesn't exist
  error: Could not register probes
  ld: error creating dtrace DOF section for architecture x86_64

The failure is explained in 8c8ed03850208e4 ("net/colo: Match is-enabled
probe to tracepoint"). In short, is-enabled probe can't be used without
a matching trace probe. And for this particular case
tpm_util_show_buffer probe should be enabled to print TPM buffer.

Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>