[clang] Revert parentesized aggregate initalization patches

This feature causes clang to crash when compiling Chrome - see
https://crbug.com/1405031 and
https://github.com/llvm/llvm-project/issues/59675

Revert "[clang] Fix a clang crash on invalid code in C++20 mode."

This reverts commit 32d7aae0.

Revert "[clang] Remove overly restrictive aggregate paren init logic"

This reverts commit c77a91bb.

Revert "[clang][C++20] P0960R3 and P1975R0: Allow initializing aggregates from a parenthesized list of values"

This reverts commit 40c52159.