Rust: clean up QLDB from Cargo Workspace members

[toof-jp]

This pull request removes the qldb entry from rustv1/examples/Cargo.toml’s workspace members. The QLDB example directory is already gone #7548, so cargo build currently fails with "error: failed to load manifest for workspace member" Dropping the stale member lets the workspace build succeed again.

$ cargo b
error: failed to load manifest for workspace member `/home/toof/ghq/github.com/awsdocs/aws-doc-sdk-examples/rustv1/examples/ql
db`
referenced by workspace at `/home/toof/ghq/github.com/awsdocs/aws-doc-sdk-examples/rustv1/examples/Cargo.toml`

Caused by:
  failed to read `/home/toof/ghq/github.com/awsdocs/aws-doc-sdk-examples/rustv1/examples/qldb/Cargo.toml`

Caused by:
  No such file or directory (os error 2)

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