Revert "[ir] Enable the IR by default"

This reverts commit b2c9d0a8dabeb8c2d62f24934c3c2e1afc0dd3ef.

Reason for revert: Doing some binary size investigation. 

Original change's description:
> [ir] Enable the IR by default
>
> This CL flips the configuration to build the IR by default instead of
> disabling by default. This is a precursor to enabling the IR more widely
> for backend generation.
>
> Bug: tint:1718
> Change-Id: I3927ce76dec29a679d723a6443ef814ace3d47fe
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/148060
> Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
> Kokoro: Kokoro <noreply+kokoro@google.com>
> Reviewed-by: James Price <jrprice@google.com>
> Reviewed-by: Ben Clayton <bclayton@google.com>

TBR=dsinclair@chromium.org,bclayton@google.com,jrprice@google.com,noreply+kokoro@google.com,dawn-scoped@luci-project-accounts.iam.gserviceaccount.com

Change-Id: I441d4a782d05e10a399cedbe810e27f8e922eda5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: tint:1718
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/148084
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
diff --git a/scripts/tint_overrides_with_defaults.gni b/scripts/tint_overrides_with_defaults.gni
index f900529..dca626e 100644
--- a/scripts/tint_overrides_with_defaults.gni
+++ b/scripts/tint_overrides_with_defaults.gni
@@ -84,7 +84,7 @@
 
   # Build the Tint IR
   if (!defined(tint_build_ir)) {
-    tint_build_ir = true
+    tint_build_ir = false
   }
 
   # Build unittests