[Core] Remove code paths that contains plasma store executable

[suquark]

Why are these changes needed?

Currently, plasma running as thread actually has been enabled by default (because java launches Ray using python scripts). Some critical functions like object spilling are also assuming that plasma store is running as a thread. So the outdated code path is no longer used and it is not functioning correctly.

However, some C++ tests are using plasma store running as a process for testing, this is not good because they are not testing what we are currently using. This PR removes the outdated plasma store executable and migrates those tests. This also reduces the size of our wheel build.

This PR may be required to pass some tests in #14924

Related issue number

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[rkooo567]

Nice change!!