Revert [llvm-objcopy] Allow strip symtab from executables and DSOs

This reverts r365193 (git commit 194f16b3)

This patch doesn't work with binaries built w/ `--emit-relocs`, e.g.

```
$ echo 'int main() { return 0; }' | clang -Wl,--emit-relocs -x c - -o foo && llvm-objcopy --strip-unneeded foo
llvm-objcopy: error: 'foo': not stripping symbol '__gmon_start__' because it is named in a relocation
```

llvm-svn: 365712