remove obsolete code in SNS MSVQ encoder

• Related issues: -
• Requested reviewers: @fotopoulou

Reason why this change is needed

Removes unnecessary code from the SNS MSVQ encoder function.

Description of the change

Moving in the SNS input parameters into the buffer that is used and the M/S processing is done twice and needs to be done only once.

Affected operating points

• BE
• No effect on bitstream