Keep bundled binutil scripts but not downloading actual binaries by default.
Automatic downloading of binutils has been causing problems for some users:
see #164, #412, #440.
Using bundled binutils helps reduce linking time, but packager codebase is
relatively small, so the gain is not significant.
Local testing shows that the full build time increases from 1m42s to 1m50s, i.e.
an increase of about 8s, or ~8%.
User can still enable the usage of bundled binutils by running
'python src/packager/third_party/binutils/download.py' and set
'linux_use_bundled_binutils' and 'linux_use_bundled_gold' to 1 in GYP_DEFINES.
Change-Id: I7ecae2333861f41054f957d0a6081dae948167bd
9b655189cf