autotools: retire conditional for debug build

likely added by mistake, the functionality works through `--enable-debug`
instead.

configure.ac

@@ -569,7 +569,6 @@ AC_CHECK_HEADERS([sys/wait.h], [HAVE_SYS_WAIT_H=1])
 AM_CONDITIONAL(WITH_PCRE2_8, test "x$enable_pcre2_8" = "xyes")
 AM_CONDITIONAL(WITH_PCRE2_16, test "x$enable_pcre2_16" = "xyes")
 AM_CONDITIONAL(WITH_PCRE2_32, test "x$enable_pcre2_32" = "xyes")
-AM_CONDITIONAL(WITH_DEBUG, test "x$enable_debug" = "xyes")
 AM_CONDITIONAL(WITH_REBUILD_CHARTABLES, test "x$enable_rebuild_chartables" = "xyes")
 AM_CONDITIONAL(WITH_JIT, test "x$enable_jit" = "xyes")
 AM_CONDITIONAL(WITH_UNICODE, test "x$enable_unicode" = "xyes")