int: No longer force disabling of fmt exceptions (#5118)

I think forcing fmt to disable exceptions is probably doing more harm
than good, probably does not work as expected for apps that use fmt
elsewhere (when we first started using fmt, it was not super popular, so
we weren't really concerned about how we might conflict with other
libraries in the same app), and disabling exceptions makes it behave
differently than std::format/print.

So let's stop doing this and see what happens! (In main.)

Also, declutter by removing the FMT_USE_GRISU definition, which was only
meaningful for very old fmt versions that are older than our minimum
supported version now.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/include/OpenImageIO/detail/fmt.h

@@ -14,11 +14,6 @@
 #    define FMT_HEADER_ONLY
 #endif
 
-// Disable fmt exceptions
-#ifndef FMT_EXCEPTIONS
-#    define FMT_EXCEPTIONS 0
-#endif
-
 #if OIIO_VERSION_LESS(3, 1, 2)
 /* DEPRECATED -- remove at next ABI compatibility boundary */
 OIIO_NAMESPACE_3_1_BEGIN
@@ -29,12 +24,6 @@ log_fmt_error(const char* message);
 OIIO_NAMESPACE_3_1_END
 #endif
 
-// Use the grisu fast floating point formatting for old fmt versions
-// (irrelevant for >= 7.1).
-#ifndef FMT_USE_GRISU
-#    define FMT_USE_GRISU 1
-#endif
-
 // fmt 8.1 stopped automatically enabling formatting of anything that supports
 // ostream output. This breaks a lot! Re-enable this old behavior.
 // NOTE: fmt 10.0 removed this support entirely.