Drop "ld command" from --info

For a long time GHC has recorded the name of the linker executable in its settings file and exposed this information via --info. Cabal previously used this for object merging but with the introduction of #20712 (closed) this is no longer necessary. We should be discouraging downstream users from any temptation to invoke the linker on their own. Afterall, linking is tricky business which only GHC knows how to do correctly. Consequently, we should drop "ld command" from --info and, after doing so, can drop some logic from configure as well.