Revert of Add Windows 10 build number to user-agent (patchset #1 id:1 of...

Revert of Add Windows 10 build number to user-agent (patchset #1 id:1 of https://codereview.chromium.org/2533303003/ )

Reason for revert:
This can cause services expecting a Windows user-agent of only two version tokens (10.0) to break.

Original issue's description:
> Add Windows 10 build number to user-agent
>
> The build number would be added to the version string in UA
> only if the major version of Windows is equal or greater than 10.
> Nothing would be changed for the old version of Windows.
>
> BUG=664622
>
> Committed: https://crrev.com/bb034491431fa28ce9b2be66b17c0417dffebc13
> Cr-Commit-Position: refs/heads/master@{#437532}

TBR=jochen@chromium.org,dcheng@chromium.org,pkasting@chromium.org,rbyers@chromium.org,ratsunny@gmail.com
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=664622, 674723

Review-Url: https://codereview.chromium.org/2581033002
Cr-Commit-Position: refs/heads/master@{#438996}

base/sys_info_win.cc

@@ -153,7 +153,7 @@ void SysInfo::OperatingSystemVersionNumbers(int32_t* major_version,
   win::OSInfo* os_info = win::OSInfo::GetInstance();
   *major_version = os_info->version_number().major;
   *minor_version = os_info->version_number().minor;
-  *bugfix_version = os_info->version_number().build;
+  *bugfix_version = 0;
 }
 
 }  // namespace base

content/common/user_agent.cc

@@ -63,15 +63,6 @@ std::string BuildOSCpuInfo() {
 #endif
 
 #if defined(OS_WIN)
-  std::string windows_version_str;
-  if (os_major_version >= 10) {
-    base::StringAppendF(&windows_version_str, "%d.%d.%d",
-      os_major_version, os_minor_version, os_bugfix_version);
-  } else {
-    base::StringAppendF(
-      &windows_version_str, "%d.%d", os_major_version, os_minor_version);
-  }
-
   std::string architecture_token;
   base::win::OSInfo* os_info = base::win::OSInfo::GetInstance();
   if (os_info->wow64_status() == base::win::OSInfo::WOW64_ENABLED) {
@@ -117,8 +108,9 @@ std::string BuildOSCpuInfo() {
   base::StringAppendF(
       &os_cpu,
 #if defined(OS_WIN)
-      "Windows NT %s%s",
-      windows_version_str.c_str(),
+      "Windows NT %d.%d%s",
+      os_major_version,
+      os_minor_version,
       architecture_token.c_str()
 #elif defined(OS_MACOSX)
       "Intel Mac OS X %d_%d_%d",