Revert of Make __DATE__ and __TIME__ to evaluate to an empty string. (patchset #5 id:80001 of https://codereview.chromium.org/2255093004/ )

Reason for revert:
This introduces a clang crash when pch are used.  See: https://llvm.org/bugs/show_bug.cgi?id=29119

Original issue's description:
> Make __DATE__ and __TIME__ to evaluate to an empty string.
>
> If __DATE__ or __TIME__ used in code, current date or time will be
> filled.  Such a value may change compile by compile, and breaks
> deterministic build.
>
> BUG=314403
>
> Committed: https://crrev.com/43088a9ef885a695061a49bcd0992cbce00a7568
> Cr-Commit-Position: refs/heads/master@{#414018}

TBR=maruel@chromium.org,dpranke@google.com,dpranke@chromium.org,rohitrao@chromium.org,thakis@chromium.org,yyanagisawa@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=314403
NOTRY=TRUE

Review-Url: https://codereview.chromium.org/2277783002
Cr-Original-Commit-Position: refs/heads/master@{#414120}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 3732ccadd4239a580746978396b8c69e9901f146

config/compiler/BUILD.gn

@@ -166,15 +166,6 @@ config("compiler") {
     # Common GCC compiler flags setup.
     # --------------------------------
     cflags += [ "-fno-strict-aliasing" ]  # See http://crbug.com/32204
-
-    # Eliminate build metadata (__DATE__ and __TIME_) for deterministic build.
-    # See https://crbug.com/314403
-    cflags += [
-      "-Wno-builtin-macro-redefined",
-      "-D__DATE__=",
-      "-D__TIME__=",
-    ]
-
     cflags_cc += [
       # If this is removed then remove the corresponding /Zc:threadSafeInit- for
       # Windows.