win: Remove printfs from net/proxy/dhcp unittests.

win: Remove printfs from net/proxy/dhcp unittests.

One of the printfs uses %d with a size_t, which isn't correct on
64bit builds. Since tests shouldn't print anyway, just delete all
printfs from this file. Fixes this clang warning:

..\..\net\proxy\dhcp_proxy_script_fetcher_win_unittest.cc(87,59) :  warning(clang): format specifies type 'int' but the argument has type 'size_type' (aka 'unsigned long long') [-Wformat]
    printf("Result code %d PAC data length %d\n", result, pac_text_.size());
                                           ~~             ^~~~~~~~~~~~~~~~
                                           %llu
1 warning generated.

BUG=82385

Review URL: https://codereview.chromium.org/755313008

Cr-Commit-Position: refs/heads/master@{#305780}