Cleanup redundant mime_util.h includes

Should make clearer the remaining dependencies of net/ on mime_util.h

BUG=none

Review URL: https://codereview.chromium.org/1028233004

Cr-Commit-Position: refs/heads/master@{#322289}

net/base/filename_util.cc

@@ -13,7 +13,6 @@
 #include "base/threading/thread_restrictions.h"
 #include "net/base/escape.h"
 #include "net/base/filename_util_internal.h"
-#include "net/base/mime_util.h"
 #include "net/base/net_string_util.h"
 #include "net/http/http_content_disposition.h"
 #include "url/gurl.h"

net/base/mime_sniffer.cc

@@ -100,7 +100,6 @@
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/string_util.h"
-#include "net/base/mime_util.h"
 #include "url/gurl.h"
 
 namespace net {

net/url_request/url_request_http_job.cc

@@ -19,7 +19,6 @@
 #include "base/time/time.h"
 #include "net/base/host_port_pair.h"
 #include "net/base/load_flags.h"
-#include "net/base/mime_util.h"
 #include "net/base/net_errors.h"
 #include "net/base/net_util.h"
 #include "net/base/network_delegate.h"