Revert "Allow more concurrent link for linux_chromium_rel_ng builder"

This reverts commit 848e109661ef338dedcd8d2d59f281308b9ec1c9.

Reason for revert: chromeos trybots are all failing compiles.

Bug: 807145
NOTRY=true

Original change's description:
> Allow more concurrent link for linux_chromium_rel_ng builder
> 
> I took peak memory usage stats for top3 largest binary link using the same args.gn with linux_chromium_rel_ng.
> 229MB chrome: 2.22 GB peak memory
> 260MB browser_tests: 2.56 GB peak memory
> 258MB unit_tests: 2.57 GB peak memory
> 
> So 3GB is sufficient.
> 
> This will help to speed up build like below.
> https://ci.chromium.org/buildbot/tryserver.chromium.linux/linux_chromium_rel_ng/634117
> ninja trace: https://chromium-build-stats.appspot.com/ninja_log/2018/01/29/slave645-c4/ninja_log.slave645-c4.chrome-bot.20180129-023145.30339.gz/trace.html
> Some newlib_pnacl related binary prevent mksnapshot to be linked due to small link pool and many targets indirectly depends on mksnapshot.
> 
> 
> Change-Id: I7c58aec10949c350bbce0a97704048caf44f5b96
> Reviewed-on: https://chromium-review.googlesource.com/891043
> Reviewed-by: Dirk Pranke <dpranke@chromium.org>
> Commit-Queue: Takuto Ikuta <tikuta@google.com>
> Cr-Commit-Position: refs/heads/master@{#532662}

TBR=thakis@chromium.org,dpranke@chromium.org,tikuta@google.com

Change-Id: I3d6a0cdc7df943731755f926ab0a5d3a0670bb5f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/891844
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#532744}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 1c99068c887584d085d0ea13370d3f6dab67f8b5

toolchain/concurrent_links.gni

@@ -35,8 +35,6 @@ if (concurrent_links == -1) {
     _args = [ "--mem_per_link_gb=4" ]
   } else if (is_android && !is_component_build && symbol_level == 2) {
     _args = [ "--mem_per_link_gb=25" ]
-  } else if (is_linux && symbol_level == 1) {
-    _args = [ "--mem_per_link_gb=3" ]
   } else {
     _args = []
   }