chipset-cnl: remove i915 flag for fastboot

i915.fastboot=1 was added as a workaround for a link training issue that
we've debugged completely and patched in the kernel. We can safely
remove this now.

Signed-off-by: Benson Leung <bleung@chromium.org>

BUG=b:71815291, b:73966543, b:70725562
TEST=boot cnl board to graphics, check that eDP panel does not have link
training issues.

Change-Id: I47d943bc5e4f11382a740a1be4879014bd8f3216
Reviewed-on: https://chromium-review.googlesource.com/951848
Commit-Ready: Benson Leung <bleung@google.com>
Tested-by: Benson Leung <bleung@google.com>
Reviewed-by: Ben Zhang <benzh@chromium.org>
Reviewed-by: Matthew S Atwood <matthew.s.atwood@intel.corp-partner.google.com>
(cherry picked from commit 2fe3e6e14e3fcf6c020c91dd29790391268ef16f)
Reviewed-on: https://chromium-review.googlesource.com/952375
Commit-Queue: Benson Leung <bleung@chromium.org>
Tested-by: Benson Leung <bleung@chromium.org>
Trybot-Ready: Benson Leung <bleung@chromium.org>
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>
diff --git a/chipset-cnl/scripts/build_kernel_image.sh b/chipset-cnl/scripts/build_kernel_image.sh
index 1e5ef90..09467cb 100755
--- a/chipset-cnl/scripts/build_kernel_image.sh
+++ b/chipset-cnl/scripts/build_kernel_image.sh
@@ -6,5 +6,4 @@
 
 modify_kernel_command_line() {
   echo "i915.alpha_support=1" >> "$1"
-  echo "i915.fastboot=1" >> "$1"
 }