wininet: Fix memory leak in HTTP_DeleteCustomHeader.

Free the memory associated with the field and value of the custom
header otherwise it will be leaked. Found by Valgrind.

dlls/wininet/http.c

diff --git a/dlls/wininet/http.c b/dlls/wininet/http.c
index 79e3511..10fa8a5 100644
--- a/dlls/wininet/http.c
+++ b/dlls/wininet/http.c
@@ -4141,6 +4141,9 @@
         return FALSE;
     lpwhr->nCustHeaders--;
 
+    HeapFree(GetProcessHeap(), 0, lpwhr->pCustHeaders[index].lpszField);
+    HeapFree(GetProcessHeap(), 0, lpwhr->pCustHeaders[index].lpszValue);
+
     memmove( &lpwhr->pCustHeaders[index], &lpwhr->pCustHeaders[index+1],
              (lpwhr->nCustHeaders - index)* sizeof(HTTPHEADERW) );
     memset( &lpwhr->pCustHeaders[lpwhr->nCustHeaders], 0, sizeof(HTTPHEADERW) );