tools: fix compilation after V8 upgrade

V8 now requires ICU's regular expressions.

PR-URL: #21983
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

tools/icu/icu-generic.gyp

@@ -32,7 +32,6 @@
       'direct_dependent_settings': {
         'defines': [
           'UCONFIG_NO_SERVICE=1',
-          'UCONFIG_NO_REGULAR_EXPRESSIONS=1',
           'U_ENABLE_DYLOAD=0',
           'U_STATIC_IMPLEMENTATION=1',
           'U_HAVE_STD_STRING=1',