IDL compiler: remove constant unpacking

The Perl IDL code generator converts hex literals to signed decimal literals.
This seems very wrong, and barely used, so this CL removes it.
This is not just a cosmetic change (potentially changes behavior),
hence it's a separate cleanup CL.

This conversion unnecessary, since hex literals are valid C++, and the single
line that does this has many bugs (only hex literals starting '0x', not
'0X' or octal or decimal or signed hex).
Further, it does this even for *unsigned* constants!

The only semantic difference is that NodeFilter has unsigned 0xFFFFFFFF,
which is converted to -1 ...and then presumably back to unsigned.

See extended discussion:
https://codereview.chromium.org/23068032/diff/15001/Source/bindings/scripts/code_generator_v8.py

Review URL: https://chromiumcodereview.appspot.com/23137023

git-svn-id: svn://svn.chromium.org/blink/trunk@156620 bbb929c8-8fbe-4397-9dbb-9b2b20218538