crashpad: Delete inconsistency with upstream

This inconsistency appears to have been introduced in error during an
update. This constant is not present in the upstream code and is unused.

Bug: crashpad:271
Change-Id: Ic1d72fe353da9076b4adf111e855347b04df3f94
Reviewed-on: https://chromium-review.googlesource.com/c/1389161Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Vlad Tsyrklevich <vtsyrklevich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619452}

third_party/crashpad/crashpad/third_party/cpp-httplib/cpp-httplib/httplib.h

@@ -39,7 +39,6 @@
 #endif
 
 typedef SOCKET socket_t;
-constexpr socket_t kInvalidSocket = INVALID_SOCKET;
 #else
 #include <pthread.h>
 #include <unistd.h>