Cleaning MSBG code

[groadabike]

@jonbarker68:

Do you know what is the point of all these level variables?

clarity/clarity/evaluator/msbg/msbg.py

Lines 210 to 217 in 6b98a25

	signal_rms_level_db = 10 * np.log10(np.mean(np.array(signal) ** 2))
	equiv_0db_spl = self.equiv_0db_spl + self.ahr
	level_db_spl = equiv_0db_spl + signal_rms_level_db
	calib_db_spl = level_db_spl
	target_spl = level_db_spl
	ref_rms_db = calib_db_spl - equiv_0db_spl

I am not sure if I am reding it correctly but there are some variables that are added and substracted making some variables useless.

for example, if we try to join all these operations in one line we get:

ref_rms_db = calib_db_spl - equiv_0db_spl 

repacing calib_db_spl

ref_rms_db = level_db_spl - equiv_0db_spl 

repacing level_db_spl

ref_rms_db = equiv_0db_spl + signal_rms_level_db - equiv_0db_spl 

obtaining

ref_rms_db = signal_rms_level_db