Remove unnecessary include in modp_b64_data.h

Currently, this file checks for a build header, just in case it defines
WORDS_BIGENDIAN. However, this build file never defines this, so it's a
useless include. This breaks attempts to depend on this library from
third party projects, namely Open Screen.

Change-Id: I9e02e530a68423af13a9a2fa0da81f4947dc37e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2481665Reviewed-by: Ryan Sleevi <rsleevi@chromium.org>
Commit-Queue: Jordan Bayles <jophba@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818627}

third_party/modp_b64/modp_b64_data.h

-#include "build/build_config.h"
 #include <stdint.h>
 
 #define CHAR62 '+'