Remove dead code

The compiler warned:
silk/float/pitch_analysis_core_FLP.c: In function 'silk_P_Ana_calc_corr_st3':
silk/float/pitch_analysis_core_FLP.c:499:36: warning: variable 'basis_ptr' set but not used [-Wunused-but-set-variable]
     const silk_float *target_ptr, *basis_ptr;

This means we can safely remove it.

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>