Remove fast PWM tweak mode
Remove fast PWM tweak mode

Fast mode was originally introduced to prevent the user seeing battery
assist mode. Now that we don't report battery assist mode to the user,
let's remove this mode to improve stability.

BUG=None
TEST=Charge with various chargers. See stable PWM duty cycles.
BRANCH=Spring

Original-Change-Id: I4a2a66e03d50dea7a28fc826369dcf2b3452007a
Signed-off-by: Vic Yang <5fd92abeee651458f98e2856f4f200ee971cee4d@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/60754
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
(cherry picked from commit 46a2073437f9a150656d37e8bd9219b01b1b3ac1)

Change-Id: I8c5b24946385576ada9f08e342beb1a70c55c974
Signed-off-by: Vic Yang <5fd92abeee651458f98e2856f4f200ee971cee4d@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/61399
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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