Remove assertion about little-endian from Base64SWAR

Summary:
It doesn't appear to actually be needed as the tests pass on big endian platforms:
#1993 (comment)

Fixes: #1993

Reviewed By: Gownta

Differential Revision: D52974667

fbshipit-source-id: 89193ec75e58d54f05e1300b56d17775aab856d2

folly/detail/base64_detail/Base64SWAR.cpp

@@ -103,9 +103,6 @@ constexpr auto kBase64SwarDecodeTable =
 template <bool isURL>
 std::uint32_t base64DecodeSWARMainLoop(
     const char*& f, const char* l, char*& o) noexcept {
-  static_assert(
-      folly::kIsLittleEndian, "Big endian requires a redesigned table");
-
   std::uint32_t errorAccumulator = 0;
 
   while (l - f > 4) {