PNaCl: Remove unused dynamic linking code from bitcode/crtbegin.c
PNaCl: Remove unused dynamic linking code from bitcode/crtbegin.c

Remove the "#ifdef SHARED" code.  Rework the comments explaining what
__dso_handle is for.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3520
TEST=PNaCl toolchain trybots

Review URL: https://codereview.chromium.org/56413003

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@12353 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client