mediapipe: removes unnecessary const

This const isn't needed and gives a compile error:

In file included from ../../third_party/mediapipe/src/mediapipe/framework/api2/node.h:8:
../../third_party/mediapipe/src/mediapipe/framework/api2/contract.h:217:22: error: 'const' type qualifier on return type has no effect [-Werror,-Wignored-qualifiers]
  217 |     static constexpr const auto get() { return (c2.*member)(); }


Bug: none
Change-Id: I71e53e8ecee2fa082e5cfa796e516abb792c40e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4777894
Reviewed-by: Robert Ogden <robertogden@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1183289}