Remove mentioned of unused LLVM patch (#57323)

Author: vchuravy

deps/patches/llvm7-symver-jlprefix.patch

@@ -250,7 +250,6 @@ For packaging Julia with LLVM, we recommend either:
  - bundling a Julia-only LLVM library inside the Julia package, or
  - adding the patches to the LLVM package of the distribution.
    * A complete list of patches is available in on [Github](https://github.com/JuliaLang/llvm-project) see the `julia-release/18.x` branch.
-   * The only Julia-specific patch is the lib renaming (`llvm7-symver-jlprefix.patch`), which should _not_ be applied to a system LLVM.
    * The remaining patches are all upstream bug fixes, and have been contributed into upstream LLVM.
 
 Using an unpatched or different version of LLVM will result in errors and/or poor performance.