Further refactored the echo suppressor code:
-Extended the InverseFft function to be more generally
 applicable.
-Included the previous external extra scaling into the
 preexisting InverseFft call.
-Moved the updating of aec->delayEstCtr to where it is
 actually used.
-Refactored the output production and comfort noise
 addition using the InverseFft function.
-Removed the if-statements checking the value of the
 constant flagHbandCn as any value different from 1 would
 crash the program. Also removed the constant

The changes have been tested for bitexactness.

BUG=webrtc:5201

Review URL: https://codereview.webrtc.org/1492343002

Cr-Commit-Position: refs/heads/master@{#11054}