Remove external/pffft/.gitmodules and submodule directories. am: 2d0d66f988 am: 74e9dacf5c am: e23fdcccfd

Original change: https://android-review.googlesource.com/c/platform/external/pffft/+/1830698

Change-Id: Ic72d8836e3937bfe8024e6815b3a7eaa6545d85b