doc: remove benchmarking section from docs

This section does not exist anymore.

Signed-off-by: Anas Nashif <[email protected]>

Author: nashif

doc/guides/porting/arch.rst

@@ -869,12 +869,6 @@ Userspace
 .. doxygengroup:: arch-userspace
    :project: Zephyr
 
-Benchmarking
-============
-
-.. doxygengroup:: arch-benchmarking
-   :project: Zephyr
-
 Memory Management
 =================