[ELF] -Map: Print symbols which needs canonical PLT entry/copy relocation just once

If a copy related symbol (say `copy`) is referenced in two .o
files, this change removes a duplicated line from the -Map output:

```
          202470           202470        1     1 .bss.rel.ro
          202470           202470        1     1         <internal>:(.bss.rel.ro)
          202470           202470        1     1                 copy
removed   202470           202470        1     1                 copy
```

Differential Revision: https://reviews.llvm.org/D115697