fix protos in another dir + a module that uses it

Protos in another directory were using import prefix, which was
prepending the repository-relative path with the value, instead, we want
to strip the prefix of the directory of the module the protos were used
in such that they can be referenced at the appropriate relative path.

Reference on import_prefix:
https://bazel.build/reference/be/protocol-buffer#proto_library.import_prefix

Test: b build //packages/modules/adb:libfastdeploy_host
Change-Id: If050b0f5fc5103bd9cc5a99703bd604325aa4204