[lldb][docs] Remove syntax hint from some output blocks

This tries to parse the block as that language but in these
cases fails because they aren't purely that language. This
falls back to a permissive mode which is fine, but highlights
the invalid tokens like errors which isn't great.

Instead don't try to highlight these blocks. This fixes 4
warnings seen in the docs build:
lldb/docs/use/tutorials/custom-frame-recognizers.md:43: WARNING: Lexing literal_block <...> as "c++" resulted in an error at token: '#'. Retrying in relaxed mode.
lldb/docs/use/tutorials/script-driven-debugging.md:175: WARNING: Lexing literal_block <...> as "c++" resulted in an error at token: '#'. Retrying in relaxed mode.
lldb/docs/use/tutorials/script-driven-debugging.md:426: WARNING: Lexing literal_block <...> as "c++" resulted in an error at token: '#'. Retrying in relaxed mode.
lldb/docs/use/tutorials/writing-custom-commands.md:416: WARNING: Lexing literal_block <...> as "python3" resulted in an error at token: '$'. Retrying in relaxed mode.

Author: DavidSpickett

lldb/docs/use/tutorials/custom-frame-recognizers.md

@@ -33,14 +33,14 @@ It's important to restrict the recognizer to the libc library (which is
 `libsystem_kernel.dylib` on macOS) to avoid matching functions with the same name
 in other modules:
 
-```c++
+```
 (lldb) command script import .../fd_recognizer.py
 (lldb) frame recognizer add -l fd_recognizer.LibcFdRecognizer -n read -s libsystem_kernel.dylib
 ```
 
 When the program is stopped at the beginning of the 'read' function in libc, we can view the recognizer arguments in 'frame variable':
 
-```c++
+```
 (lldb) b read
 (lldb) r
 Process 1234 stopped

lldb/docs/use/tutorials/script-driven-debugging.md

@@ -172,7 +172,7 @@ At this point we are ready to use the DFS function to see if the word "Romeo"
 is in our tree or not. To actually use it in LLDB on our dictionary program,
 you would do something like this:
 
-```c++
+```
 $ lldb
 (lldb) process attach -n "dictionary"
 Architecture set to: x86_64.
@@ -423,7 +423,7 @@ Enter your Python command(s). Type 'DONE' to end.
 >     print "Here is the problem. Going right, should go left!"
 > DONE
 ```
-```c++
+```
 (lldb) continue
 Process 696 resuming
 Here is the problem. Going right, should go left!

lldb/docs/use/tutorials/writing-custom-commands.md

@@ -413,7 +413,7 @@ you may want a `pofoo` X command, that equates po [ModifyString(X)
 capitalizedString]. The following debugger interaction shows how to achieve
 that goal:
 
-```python3
+```
 (lldb) script
 Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.
 >>> def pofoo_funct(debugger, command, result, internal_dict):