util: stop using time.perf_counter() for timer()

Summary:
Some code paths (ex. metalog.commit) use `util.timer()` as a way to get
seconds since epoch, and get 0 for tests. Other use-cases of `util.timer()`
are ad-hoc time measure for displaying speed / progress. They do not need high
precision or strong guarantee that the clock does not go backwards. Drop the
`time.perf_counter()` to meet the first use-case's expectation.

Reviewed By: singhsrb

Differential Revision: D23431253

fbshipit-source-id: 8bf2d1ed32e284e17285742e1d0fd7178f181fb3

Author: quark-zju

eden/scm/edenscm/mercurial/util.py

@@ -1388,13 +1388,7 @@ def _reloadenv():
 
     global timer, getuser, istest
 
-    if pycompat.iswindows:
-        timer = time.clock
-    else:
-        timer = time.time
-
-    if safehasattr(time, "perf_counter"):
-        timer = time.perf_counter
+    timer = time.time
 
     if "TESTTMP" in os.environ or "testutil" in sys.modules:
         # Stabilize test output