Fix error header for bidirectional streaming models

[SergeyRyabinin]

Issue #, if available:
Modeled errors that can be represented using a common error shape are not generated in CPP SDK, but still were referenced on some supposedly unused headers.
These unused headers is a different issue to be fixed.

Description of changes:
Change the type of certain errors referenced so they do exist.
Tested using #3391

PS: I've also tried to generate the following block in the errors header:

namespace Model {
using BadRequestException = Aws::Client::AWSError<TranscribeStreamingServiceErrors>;
using ConflictException = Aws::Client::AWSError<TranscribeStreamingServiceErrors>;
using InternalFailureException = Aws::Client::AWSError<TranscribeStreamingServiceErrors>;
using LimitExceededException = Aws::Client::AWSError<TranscribeStreamingServiceErrors>;
using ResourceNotFoundException = Aws::Client::AWSError<TranscribeStreamingServiceErrors>;
using ServiceUnavailableException = Aws::Client::AWSError<TranscribeStreamingServiceErrors>;
}  // namespace Model

However, the problem is that this block would be generated for almost any service present, unless a more complicated logic (if such error is present AND referenced by some other shape) is required to avoid huge diff.
Check all that applies:

• Did a review by yourself.
• Added proper tests to cover this PR. (If tests are not applicable, explain.)
• Checked if this PR is a breaking (APIs have been changed) change.
• Checked if this PR will not introduce cross-platform inconsistent behavior.
• Checked if this PR would require a ReadMe/Wiki update.

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