remove repetitive code

[cuishuang]

It seems that only one definition is needed here, but two definitions are accidentally included

[rustbot]

r? @TaKO8Ki

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[rust-log-analyzer]

The job x86_64-gnu-tools failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

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GOROOT_1_19_X64=/opt/hostedtoolcache/go/1.19.13/x64
---
604 |                       where_clauses: (
    |  ____________________________________^
605 | |                         ast::TyAliasWhereClause::default(),
606 | |                     ),
    | |_____________________^ expected a tuple with 2 elements, found one with 1 element
    |
    = note: expected tuple `(TyAliasWhereClause, TyAliasWhereClause)`
               found tuple `(TyAliasWhereClause,)`
For more information about this error, try `rustc --explain E0308`.
error: could not compile `rustc_builtin_macros` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
Build completed unsuccessfully in 0:01:40

[ValShaped]

It looks like the two TyAliasWhereClauses are required. As noted in this comment, (rustc_ast/src/ast.rs#L3016,) they refer to different sides of the same type alias.

[bors]

☔ The latest upstream changes (presumably #121810) made this pull request unmergeable. Please resolve the merge conflicts.

[cuishuang]

It looks like the two TyAliasWhereClauses are required. As noted in this comment, (rustc_ast/src/ast.rs#L3016,) they refer to different sides of the same type alias.

Thanks for the guidance, sorry to disturb you, I will close this PR