drm/imagination: Removed unused functions in pvr_fw_trace

drm/imagination: Removed unused functions in pvr_fw_trace

Fixing the warning below due to an unused file level vtable. Removing
only this causes additional warnings for the now unused functions, so
I've removed those too.

>> drivers/gpu/drm/imagination/pvr_fw_trace.c:205:37: warning: 'pvr_fw_trace_group_mask_fops' defined but not used [-Wunused-const-variable=]
     205 | static const struct file_operations pvr_fw_trace_group_mask_fops = {
         |                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

Changes since v1:
- Corrected hash in Fixes tag.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202311302054.MVYPxFCE-lkp@intel.com/
Fixes: cb56cd610866 ("drm/imagination: Add firmware trace to debugfs")
Signed-off-by: Donald Robson <donald.robson@imgtec.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231204151337.60930-1-donald.robson@imgtec.com