Fix several instances of doubled words

One in an exception; the rest in docblocks.
merged branch jbafford/doubled-word-fixes (PR #8144)

This PR was merged into the 2.1 branch.

Discussion
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Fix several instances of doubled words

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

One correction to an exception; the rest in docblocks.

Commits
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52fed7b Fix several instances of doubled words