Remove Googletest FAQ entry for obsolete ProtocolMessageEquals and ProtocolMessageEquiv

* These long-dead variants of the proto matchers don't exist in the current version of Googletest.
* No evidence of external usage: [the only external references I see](https://www.google.com/search?q=%22protocolmessageequals%22+OR+%22protocolmessageequals%22) are copies of this guide. Possibly they were already removed by the time Googletest was publicly released.

PiperOrigin-RevId: 565358401
Change-Id: I61379b7333fa8ee19cd5520caedf2c539f54c2d7

Author: Michael Hirshleifer

docs/faq.md

@@ -128,27 +128,6 @@ both approaches a try. Practice is a much better way to grasp the subtle
 differences between the two tools. Once you have some concrete experience, you
 can much more easily decide which one to use the next time.
 
-## I got some run-time errors about invalid proto descriptors when using `ProtocolMessageEquals`. Help!
-
-{: .callout .note}
-**Note:** `ProtocolMessageEquals` and `ProtocolMessageEquiv` are *deprecated*
-now. Please use `EqualsProto`, etc instead.
-
-`ProtocolMessageEquals` and `ProtocolMessageEquiv` were redefined recently and
-are now less tolerant of invalid protocol buffer definitions. In particular, if
-you have a `foo.proto` that doesn't fully qualify the type of a protocol message
-it references (e.g. `message<Bar>` where it should be `message<blah.Bar>`), you
-will now get run-time errors like:
-
-```
-... descriptor.cc:...] Invalid proto descriptor for file "path/to/foo.proto":
-... descriptor.cc:...]  blah.MyMessage.my_field: ".Bar" is not defined.
-```
-
-If you see this, your `.proto` file is broken and needs to be fixed by making
-the types fully qualified. The new definition of `ProtocolMessageEquals` and
-`ProtocolMessageEquiv` just happen to reveal your bug.
-
 ## My death test modifies some state, but the change seems lost after the death test finishes. Why?
 
 Death tests (`EXPECT_DEATH`, etc) are executed in a sub-process s.t. the