configure: Don't check LD -v --help for LIBC_LINKER_FEATURE

When LIBC_LINKER_FEATURE is used to check a linker option with the equal
sign, it will likely fail because the LD -v --help output may look like
`-z lam-report=[none|warning|error]` while the needle is something like
`-z lam-report=warning`.

The LD -v --help filter doesn't save much time, so just remove it.