Revert "Enable icu-timezone-data by default"

This reverts commit d9a25842.

Reason for revert: 

I'm reverting this CL for a few reasons. #2 is the most significant and I should have thought of that before making a switch. Sorry for that.   

1) perf-regression: http://crbug.com/769706
2) http://crbug.com/612010 : ICU timezone update is not propagated to zygote process so that new tabs will hold on to an old timezone even after a timezone change on Linux and Chrome OS. 
3) http://crbug.com/754053 : OS timezone detection issues on macOS 10.13, Ubutu 16, RHEL 7, SuSe Linux 12 or newer. ; it's being fixed. So, it actually ok.  
4) http://crbug.com/771868 : timezone wrong in gmail: If it's due to #3, we're fine because it's fixed. If not, we need to look more.

Original change's description:
> Enable icu-timezone-data by default
> 
> This will introduce a new behavior on POSIX(-like) platforms. Timezone
> names inside parentheses after GMT offset will not be 3-4 letter
> abbreviation any longer. They'll be human-readable names in the current
> default locale. This matches the current Windows behavior.
> 
> new Date(2017, 5, 22).toString()
> new Date(2017, 11, 22).toString()
> 
> Current:
> 
> Thu Jun 22 2017 00:00:00 GMT-0700 (PDT)
> Fri Dec 22 2017 00:00:00 GMT-0800 (PST)
> 
> New in en-US locale:
> 
> Thu Jun 22 2017 00:00:00 GMT-0700 (Pacific Daylight Time)
> Fri Dec 22 2017 00:00:00 GMT-0800 (Pacific Standard Time)
> 
> New in German locale:
> 
> Thu Jun 22 2017 00:00:00 GMT-0700 (Nordamerikanische Westküsten-Sommerzeit)
> Fri Dec 22 2017 00:00:00 GMT-0800 (Nordamerikanische Westküsten-Normalzeit)
> 
> BUG=v8:6031, v8:2137, v8:6076
> TEST=mjsunit/icu-date-lord-howe.js, mjsunit/icu-date-to-string.js
> 
> Change-Id: I4e7fd8b3ddae5c7779e220c4c101e45904fcdc01
> Reviewed-on: https://chromium-review.googlesource.com/625164
> Commit-Queue: Jungshik Shin <jshin@chromium.org>
> Reviewed-by: Daniel Ehrenberg <littledan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#47953}

TBR=adamk@chromium.org,littledan@chromium.org,jshin@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:6031, v8:2137, v8:6076, chromium:769706, chromium:612010, chromium:771868
Change-Id: I60d75467ee21975d3a235344b01c0d2d44a7da96
Reviewed-on: https://chromium-review.googlesource.com/713404Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Jungshik Shin <jshin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48478}

src/flag-definitions.h

@@ -266,7 +266,8 @@ HARMONY_SHIPPING(FLAG_SHIPPING_FEATURES)
 #undef FLAG_SHIPPING_FEATURES
 
 #ifdef V8_INTL_SUPPORT
-DEFINE_BOOL(icu_timezone_data, true, "get information about timezones from ICU")
+DEFINE_BOOL(icu_timezone_data, false,
+            "get information about timezones from ICU")
 #endif
 
 #ifdef V8_ENABLE_FUTURE