[hooks] Remove unused meta dependency (fixes Flutter compat)

[brucearctor]

Problem

The hooks package lists meta: ^1.19.0 as a dependency but never imports package:meta anywhere in its lib/ or test/ directories.

This unused dependency causes version conflicts for Flutter packages that use build hooks:

Because my_package depends on hooks ^2.1.0 which depends on meta ^1.19.0,
every version of my_package requires meta ^1.19.0.
And because every version of flutter_test from sdk depends on meta 1.17.0,
my_package is incompatible with flutter_test from sdk.

Flutter stable (3.41.9, Dart 3.11.5) pins meta 1.17.0 via flutter_test. Since pub.dev enforces that hook/ imports must be in dependencies (not dev_dependencies), there is no workaround — any Flutter package using build hooks is blocked.

Verification

# Zero imports of package:meta in hooks lib/ or test/
$ grep -rn "import.*package:meta" pkgs/hooks/lib/ pkgs/hooks/test/ --include='*.dart'
# (no output)

Note: hooks_runner legitimately uses package:meta — this PR only removes it from hooks.

Fix

Remove meta: ^1.19.0 from pkgs/hooks/pubspec.yaml dependencies.

Fixes #3551

[dcharkes]

I suppose we removed @experimental or something similar and are now no longer using it. 👍

(And we bumped to 1.19 in this repo due to @RecordUse() and @mustBeConst from package:meta no longer being experimental in that version.)