This removes our own fork of `absl::StatusOr<>`. Sandboxed API still includes
a custom matcher for Googletest, as that is not open source yet. For
compatibility, the `statusor.h` header is still retained and now aliases
`sapi::StatusOr<>` to `absl::StatusOr<>`.
PiperOrigin-RevId: 329916309
Change-Id: I0544b73a9e312dce499bc4128c28457e04ab9929
Fixes some template issues that could lead to code not compiling when it
otherwise should.
PiperOrigin-RevId: 308809964
Change-Id: I9f2f9d4aff5f1a9cb967fb705a86fd7f49114f7a
