AK: Stop exporting AK::FixedPoint into the global namespace

This declaration has conflicts with the macOS SDK, which becomes a
problem when trying to interact with system clang modules.

AK/FixedPoint.h

@@ -480,7 +480,3 @@ struct Formatter<FixedPoint<precision, Underlying>> : StandardFormatter {
 };
 
 }
-
-#if USING_AK_GLOBALLY
-using AK::FixedPoint;
-#endif

AK/Forward.h

@@ -160,7 +160,6 @@ using AK::DoublyLinkedList;
 using AK::Error;
 using AK::ErrorOr;
 using AK::FixedArray;
-using AK::FixedPoint;
 using AK::FlyString;
 using AK::Function;
 using AK::GenericLexer;

Tests/AK/TestFixedPoint.cpp

@@ -9,6 +9,8 @@
 #include <AK/FixedPoint.h>
 #include <AK/NumericLimits.h>
 
+using AK::FixedPoint;
+
 using Type = FixedPoint<4>;
 
 TEST_CASE(arithmetic)