[llvm] [DataLayout] Remove `clear` and `reset` methods (NFC) (PR #102993)

[Tim Besard via llvm-commits]

maleadt wrote:

> `createDataLayout()` returns a const copy of it.

You're right, I misdiagnosed the issue (which did appear after upgrading to LLVM 20, so this change seemed likely).

https://github.com/llvm/llvm-project/pull/102993