Math: don't include FunctionsBatch.h from Functions.h anymore.

These two got split in 2019.10 but one included the other for backwards
compat. It makes everything suffer from worse compile times, so not
doing that anymore.

doc/changelog.dox

@@ -233,6 +233,9 @@ See also:
     now return a signed scaling vector instead of unsigned in order to prevent
     information loss. To restore the old behavior, apply @ref Math::abs() on
     the result.
+-   The @ref Magnum/Math/FunctionsBatch.h header is no longer included from
+    @ref Magnum/Math/Functions.h for backwards compatibility in order to speed
+    up compile times.
 -   @ref Platform::GlfwApplication::setMinWindowSize() /
     @ref Platform::GlfwApplication::setMaxWindowSize() and equivalent APIs in
     @ref Platform::Sdl2Application now premultiply the value with

src/Magnum/Math/Functions.h

@@ -658,8 +658,4 @@ template<std::size_t size, class T> inline Vector<size, T> sqrtInverted(const Ve
 
 }}
 
-#ifdef MAGNUM_BUILD_DEPRECATED
-#include "Magnum/Math/FunctionsBatch.h" /** @todo remove once compat is dropped */
-#endif
-
 #endif