[Object] Remove unneeded check in ELFFile<ELFT>::dynamicEntries().

Check for `DynSecSize % sizeof(Elf_Dyn) != 0` is unneeded in this context.

1. If the .dynamic section is acquired from program headers, the .dynamic
section is "cut off" by

```
makeArrayRef(..., Phdr.p_filesz / sizeof(Elf_Dyn));
DynSeSize = Phdr.p_filesz;
```

2. If the .dynamic section is acquired from section headers, the .dynamic
section is checked in `getSectionContentsAsArray<Elf_Dyn>(&Sec)`.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D79560