Revert rtc_dcheck_always_on.

This CL reverts:
https://webrtc-review.googlesource.com/c/src/+/226864
https://webrtc-review.googlesource.com/c/src/+/226563

Reason for revert:
See also V8 equivalent: crrev.com/c/3055294.
This has been properly fixed by crrev.com/c/3053740.
Now dcheck_always_on already defaults to false for subprojects
like WebRTC and no other switch is required. The switch didn't fully
work anyways due to https://crbug.com/1231890.

No-Try: True
Bug: chromium:1225701, webrtc:12988
Change-Id: I9888d7ac02ef2ba4fdc372de20f1d2d71f6d0299
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227021
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Andrey Logvin <landrey@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34603}

tools_webrtc/coverage/generate_ios_coverage_command.py

@@ -89,7 +89,7 @@ def GetGNArgs(is_simulator):
     target_cpu = 'x64' if is_simulator else 'arm64'
     return ([] + ['target_os="ios"'] + ['target_cpu="%s"' % target_cpu] +
             ['use_clang_coverage=true'] + ['is_component_build=false'] +
-            ['rtc_dcheck_always_on=true'])
+            ['dcheck_always_on=true'])
 
 
 def GenerateIOSSimulatorCommand():