libcamera: base: utils: Drop defopt

utils::defopt causes compilation issues on gcc 8.0.0 to gcc 8.3.0,
likely due to bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86521
that was fixed in gcc 8.4.0. gcc 8.3.0 may be considered old (libcamera
requires gcc-8 or newer), but it is shipped by Debian 10 that has LTS
support until mid-2024.

As no workaround has been found to fix compilation on gcc 8.3.0 while
still retaining the functionality of utils::defopt, remove it from the
libcamera base library. This change could be reverted once support for
gcc-8 will be dropped.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/base/utils.cpp

@@ -463,27 +463,6 @@ std::string toAscii(const std::string &str)
  * \a b
  */
 
-/**
- * \var defopt
- * \brief Constant used with std::optional::value_or() to create a
- * default-constructed object
- *
- * The std::optional<T>::value_or(U &&default_value) function returns the
- * contained value if available, or \a default_value if the std::optional has no
- * value. If the desired default value is a default-constructed T, the obvious
- * option is to call std::optional<T>::value_or(T{}). This approach has two
- * drawbacks:
- *
- * * The \a default_value T{} is constructed even if the std::optional instance
- *   has a value, which impacts efficiency.
- * * The T{} default constructor needs to be spelled out explicitly in the
- *   value_or() call, leading to long lines if the type is complex.
- *
- * The defopt variable solves these issues by providing a value that can be
- * passed to std::optional<T>::value_or() and get implicitly converted to a
- * default-constructed T.
- */
-
 } /* namespace utils */
 
 #ifndef __DOXYGEN__