Reverts build arg changes from adding SharedFuture

[jb-gcx]

Reverts parts of commit ae855ee

This change was made in #183 and it causes our CI to fail compiling protobuf. The change in .buildrc appends -fcoroutines-ts to the compilation of djinni dependencies, which definitely don't need it. As far as I understand it's only needed for tests, so we can test djinni coroutine implementations.

Example error from our CI:

  Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
  gcc: error: unrecognized command-line option '-fcoroutines-ts'; did you mean '-fcoroutines'?
  ERROR: /home/runner/.cache/bazel/_bazel_runner/a8bde27687bcb180662e14df4ed3e9b6/external/com_google_protobuf/BUILD:471:10: Compiling src/google/protobuf/compiler/main.cc failed: (Exit 1): gcc failed: error executing command /usr/bin/gcc -U_FORTIFY_SOURCE -fstack-protector -Wall -Wunused-but-set-parameter -Wno-free-nonheap-object -fno-omit-frame-pointer -g0 -O2 '-D_FORTIFY_SOURCE=1' -DNDEBUG -ffunction-sections ... (remaining 39 arguments skipped)