Revert r361630 "[llvm-readelf] - Allow dumping of the .dynamic section even if...

Revert r361630 "[llvm-readelf] - Allow dumping of the .dynamic section even if there is no PT_DYNAMIC header."

It broke BB:
http://lab.llvm.org:8011/builders/ppc64le-lld-multistage-test/builds/3748

llvm-svn: 361631