Remove outdated references to :interval suffix on wall_clock xtri…

…gger

It has no effect as `wall_clock` is specially implemented

src/tutorial/furthertopics/clock-triggered-tasks.rst

@@ -14,7 +14,8 @@ Clock-triggering effectively enables us to tether the "cycle time" to the
 .. note::
 
    Clock triggers are :ref:`Section External Triggers`. They differ from
-   custom external triggers only in that they are provided with Cylc.
+   custom external triggers only in that they are provided with Cylc, and
+   that the ``:interval`` suffix has no effect.
 
 
 Clock Triggering
@@ -135,9 +136,9 @@ Edit the ``[[scheduling]]`` section to read:
    initial cycle point = now
    final cycle point = +P1D # Run for one day
    [[xtriggers]]
-       quarter_past_trigger = wall_clock(offset=PT15M):PT30S
-       half_past_trigger = wall_clock(offset=PT30M):PT30S
-       quarter_to_trigger = wall_clock(offset=PT45M):PT30S
+       quarter_past_trigger = wall_clock(offset=PT15M)
+       half_past_trigger = wall_clock(offset=PT30M)
+       quarter_to_trigger = wall_clock(offset=PT45M)
    [[graph]]
        PT1H = """
            @wall_clock => bell
@@ -165,15 +166,6 @@ Leave your workflow running for a while to confirm it is working as expected
 before stopping it.
 
 
-.. note::
-
-   You may have noticed the ``:PT30S`` at the end of each clock trigger
-   definition. This how often the :ref:`Section External Triggers` is checked.
-   By default external triggers are checked every 10 seconds, but if there
-   are a lot of external triggers this can be hard work for the computer
-   running the workflow and it may not be necessary to check this often.
-
-
 Summary
 -------
 

src/tutorial/scheduling/further-scheduling.rst

@@ -75,7 +75,7 @@ Clock Triggers
    [scheduling]
        initial cycle point = 2000-01-01T00Z
        [[xtriggers]]
-           PT1H_trigger = wall_clock(offset=-PT1H):PT30S
+           PT1H_trigger = wall_clock(offset=-PT1H)
        [[graph]]
            # "daily" will run, at the earliest, one hour before midday.
            T12 = @PT1H_trigger => daily

src/user-guide/writing-workflows/external-triggers.rst

@@ -75,17 +75,15 @@ cycle point value by one hour:
    [scheduling]
        initial cycle point = 2018-01-01
        [[xtriggers]]
-           clock_1 = wall_clock(offset=PT1H):PT10S
+           clock_1 = wall_clock(offset=PT1H)
        [[graph]]
            P1D = "@clock_1 => foo"
    [runtime]
        [[foo]]
            script = run-foo.sh
 
 Notice that the short label ``clock_1`` is used to represent the
-trigger function in the graph. The function call interval, which determines how
-often the :term:`scheduler` checks the clock, is optional. Here it is
-``PT10S`` (i.e. 10 seconds, which is also the default value).
+trigger function in the graph.
 
 Argument keywords can be omitted if called in the right order, so the
 ``clock_1`` trigger can also be declared like this: