perf_hooks: remove docs for unimplemented API

The node frame (aka loop) timing API did not land, it depends on
libuv/libuv#1489 which is still a WIP.

See: nodejs#14680 (comment)

Author: sam-github

doc/api/perf_hooks.md

@@ -135,16 +135,6 @@ the Performance Timeline or any of the timestamp properties provided by the
 `PerformanceNodeTiming` class. If the named `endMark` does not exist, an
 error will be thrown.
 
-### performance.nodeFrame
-<!-- YAML
-added: v8.5.0
--->
-
-* {PerformanceFrame}
-
-An instance of the `PerformanceFrame` class that provides performance metrics
-for the event loop.
-
 ### performance.nodeTiming
 <!-- YAML
 added: v8.5.0
@@ -268,37 +258,6 @@ The value may be one of:
 * `perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL`
 * `perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB`
 
-## Class: PerformanceNodeFrame extends PerformanceEntry
-<!-- YAML
-added: v8.5.0
--->
-
-Provides timing details for the Node.js event loop.
-
-### performanceNodeFrame.frameCheck
-
-The high resolution timestamp when `uv_check_t` processing occurred on the
-current loop.
-
-### performanceNodeFrame.frameCount
-
-The total number of event loop iterations (iterated when `uv_idle_t`
-processing occurrs).
-
-### performanceNodeFrame.frameIdle
-
-The high resolution timestamp when `uv_idle_t` processing occurred on the
-current loop.
-
-### performanceNodeFrame.framesPerSecond
-
-The number of event loop iterations per second.
-
-### performanceNodeFrame.framePrepare
-
-The high resolution timestamp when `uv_prepare_t` processing occurred on the
-current loop.
-
 ## Class: PerformanceNodeTiming extends PerformanceEntry
 <!-- YAML
 added: v8.5.0