loader: gc loader_get_extensions_name() and __DRI_DRIVER_{GET_,}EXTENSIONS defines

Leaving the defines in include/GL/internal/dri_interface.h because I'm
not sure if something needs it.

Fixes: fa541a887c ("loader: delete loader_open_driver()")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30266>

src/gallium/include/mesa_interface.h

@@ -668,25 +668,6 @@ struct __DRIuseInvalidateExtensionRec {
    __DRIextension base;
 };
 
-/**
- * Dead, do not use; kept only to allow old Xserver to compile since
- * this file is a public API.
- */
-#define __DRI_DRIVER_EXTENSIONS "__driDriverExtensions"
-
-/**
- * This symbol replaces the __DRI_DRIVER_EXTENSIONS symbol, and will be
- * suffixed by "_drivername", allowing multiple drivers to be built into one
- * library, and also giving the driver the chance to return a variable driver
- * extensions struct depending on the driver name being loaded or any other
- * system state.
- *
- * The function prototype is:
- *
- * const __DRIextension **__driDriverGetExtensions_drivername(void);
- */
-#define __DRI_DRIVER_GET_EXTENSIONS "__driDriverGetExtensions"
-
 /**
  * Tokens for __DRIconfig attribs.  A number of attributes defined by
  * GLX or EGL standards are not in the table, as they must be provided

src/loader/loader.c

@@ -732,23 +732,6 @@ loader_set_logger(loader_logger *logger)
    log_ = logger;
 }
 
-char *
-loader_get_extensions_name(const char *driver_name)
-{
-   char *name = NULL;
-
-   if (asprintf(&name, "%s_%s", __DRI_DRIVER_GET_EXTENSIONS, driver_name) < 0)
-      return NULL;
-
-   const size_t len = strlen(name);
-   for (size_t i = 0; i < len; i++) {
-      if (name[i] == '-')
-         name[i] = '_';
-   }
-
-   return name;
-}
-
 bool
 loader_bind_extensions(void *data,
                        const struct dri_extension_match *matches, size_t num_matches,

src/loader/loader.h

@@ -94,9 +94,6 @@ typedef void loader_logger(int level, const char *fmt, ...);
 void
 loader_set_logger(loader_logger *logger);
 
-char *
-loader_get_extensions_name(const char *driver_name);
-
 struct dri_extension_match {
    /* __DRI_* extension name */
    const char *name;