disk layout: remove comment requiring space for boot cache

We don't use boot cache anymore and don't need to reserve space for
it.

BUG=chromium:774738
TEST=none

Exempt-From-Owner-Approval: just a comment change + OWNERS didn't respond
Change-Id: I2ec9bc6fcfa0e53307b657cf7bfb03408cb8db70
Reviewed-on: https://chromium-review.googlesource.com/1822680
Tested-by: Sean Abraham <seanabraham@chromium.org>
Commit-Ready: Sean Abraham <seanabraham@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Sean Abraham <seanabraham@chromium.org>
diff --git a/build_library/legacy_disk_layout.json b/build_library/legacy_disk_layout.json
index 2f80c60..a5fcc4b 100644
--- a/build_library/legacy_disk_layout.json
+++ b/build_library/legacy_disk_layout.json
@@ -94,7 +94,7 @@
       },
       {
         # Slot A rootfs. Rootfs + extras must fit.
-        # FS size + Verity (64 * FS blocks) + Boot Cache (200M).
+        # FS size + Verity (64 * FS blocks).
         # Make sure that other layouts still has room for the
         # extras, should you increase FS size
         #