`$\delta p$` to `$\delta$ p`

New MR since the other one has a change to the cbor file, for some reason...

benchmarks/tracking/scripts/tracking_performance.py

@@ -186,7 +186,7 @@ if __name__ == '__main__':
                              weights=np.repeat(1./float(rec_p.shape[0]), rec_p.shape[0]), ec='k')
     nbins = hbins.shape[0] - 1
     ax.set_ylabel('Normalized Counts / {:d} Bins'.format(nbins), fontsize=20)
-    ax.set_xlabel('$\delta p$ (%)', fontsize=20)
+    ax.set_xlabel(r'$\delta$ p (%)', fontsize=20)
 
     # theta resolution
     ax = axs.flat[2]