Don't detect pre-C++11 in <openssl/base.h>

When we first added bssl::UniquePtr, we added a __cplusplus version
check to tolerate C++98 and C++03 consumers of our public headers, and
only giving them the C symbols.

It is now 2025. Since then, we've added <openssl/span.h> and written
C++17-requiring code in it, so C++11 and C++14 consumers of public
headers already broke. No longer try to bifurcate our consumer and
implementation C++ versions.

Update-Note: C++ projects including BoringSSL headers now must be C++17
or later, matching the requirement for building BoringSSL. C projects
are unaffected. C++ projects that were previously building at C++98 or
C++03 will need to update to a language version from sometime in the
last couple decades.

Change-Id: I9e6ae1807398e5363ff71e0d2a83bfaa3f8bcbfc
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/84947
Commit-Queue: Rudolf Polzer <rpolzer@google.com>
Auto-Submit: David Benjamin <davidben@google.com>
Reviewed-by: Rudolf Polzer <rpolzer@google.com>

include/openssl/base.h

diff --git a/include/openssl/base.h b/include/openssl/base.h
index 8707b54..d942427 100644
--- a/include/openssl/base.h
+++ b/include/openssl/base.h
@@ -406,13 +406,6 @@
 #define BSSL_NAMESPACE_END }
 #endif
 
-// MSVC doesn't set __cplusplus to 201103 to indicate C++11 support (see
-// https://connect.microsoft.com/VisualStudio/feedback/details/763051/a-value-of-predefined-macro-cplusplus-is-still-199711l)
-// so MSVC is just assumed to support C++11.
-#if !defined(BORINGSSL_NO_CXX) && __cplusplus < 201103L && !defined(_MSC_VER)
-#define BORINGSSL_NO_CXX
-#endif
-
 #if defined(BORINGSSL_NO_CXX)
 
 #define BORINGSSL_MAKE_DELETER(type, deleter)