[llvm] [BOLT][NFC] Clean up the outdated option --write-dwp in doc (PR #166150)

[Jinjie Huang via llvm-commits]

Jinjie-Huang wrote:

Got it, It looks like this test aims to compare the pre-BOLT and post-BOLT DWP files for consistency. A better way might be to use llvm-dwp manually and remove the outdated usage.

https://github.com/llvm/llvm-project/pull/166150