Fix phpdoc and coding standards

This removes the unused use statements which were not catched by
PHP-CS-Fixer because of string occurences. It also fixes some invalid
phpdoc (scalar is not recognized as a valid type for instance).
minor #13162 Fix phpdoc and coding standards (stof)

This PR was merged into the 2.3 branch.

Discussion
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Fix phpdoc and coding standards

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

This removes the unused use statements which were not catched by PHP-CS-Fixer because of string occurences. It also fixes some invalid phpdoc (scalar is not recognized as a valid type for instance).

This is complementary to https://github.com/symfony/symfony/pull/13134

Commits
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8cc3f6a Fix phpdoc and coding standards