Remove external/pffft/.gitmodules and submodule directories. am: 2d0d66f988 am: 74e9dacf5c am: e23fdcccfd am: 5ec369b08b

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

Change-Id: I77689a7f14c4c9c618ae663cbfddeb4f790c926e