Remove two useless attributes that snuck in while https://codereview.chromium.org/1221073004 was in…

Remove two useless attributes that snuck in while https://codereview.chromium.org/1221073004 was in review.

No intended behavior change.  Should fix these errors on the clang/win bots:

../..\components/proxy_config/proxy_prefs.h(18,6) :  error: 'dllexport' attribute only applies to variables, functions and classes [-Werror,-Wignored-attributes]
enum PROXY_CONFIG_EXPORT ProxyMode {
     ^
../..\components/proxy_config/proxy_config_export.h(12,40) :  note: expanded from macro 'PROXY_CONFIG_EXPORT'
                                       ^
In file included from ../../components/proxy_config/proxy_prefs.cc:5:
../..\components/proxy_config/proxy_prefs.h(41,6) :  error: 'dllexport' attribute only applies to variables, functions and classes [-Werror,-Wignored-attributes]
enum PROXY_CONFIG_EXPORT ConfigState {
     ^
../..\components/proxy_config/proxy_config_export.h(12,40) :  note: expanded from macro 'PROXY_CONFIG_EXPORT'
                                       ^

BUG=504695
TBR=stevenjb,benwells

Committed: https://chromium.googlesource.com/chromium/src/+/a6bb27acad7dde726d805d7ce880d85aed105869

[Nico, 2015-07-06 20:39:45]

thakis@chromium.org changed reviewers:
+ benwells@chromium.org, stevenjb@chromium.org

[Nico, 2015-07-06 20:39:48]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2015-07-06 20:40:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1218803005/1

[Nico, 2015-07-06 21:00:48]

Committed patchset #1 (id:1) manually as
a6bb27acad7dde726d805d7ce880d85aed105869 (presubmit successful).