Bug 1897030 - Remove cfg(icu4x_custom_data) check in icu_segmenter_data. r=m_kato

We don't have any facility to set it in the Firefox build, so rather than add a
build.rs to make rustc 1.80 happy, just remove the cfg.

Differential Revision: https://phabricator.services.mozilla.com/D210591

intl/icu_segmenter_data/src/lib.rs

@@ -6,7 +6,4 @@
 
 #![no_std]
 
-#[cfg(icu4x_custom_data)]
-include!(concat!(core::env!("ICU4X_DATA_DIR"), "/macros.rs"));
-#[cfg(not(icu4x_custom_data))]
 include!("../data/macros.rs");