Revert "Make doxygen buildable again (#2423)" (#2437)

This reverts commit 65a8907.

Author: lurch

src/rp2_common/pico_lwip/doc.h

@@ -51,13 +51,19 @@
  *
  * This library enables you to make use of the LwIP HTTP client and server library
  *
+ * \par LwIP HTTP server
+ *
  * To make use of the LwIP HTTP server you need to provide the HTML that the server will return to the client.
  * This is done by compiling the content directly into the executable.
  *
+ * \par makefsdata
+ *
  * LwIP provides a c-library tool `makefsdata` to compile your HTML into a source file for inclusion into your program.
  * This is quite hard to use as you need to compile the tool as a native binary, then run the tool to generate a source file
  * before compiling your code for the Pico device.
  *
+ * \par pico_set_lwip_httpd_content
+ *
  * To make this whole process easier, a python script `makefsdata.py` is provided to generate a source file for your HTML content.
  * A CMake function `pico_set_lwip_httpd_content` takes care of running the `makefsdata.py` python script for you.
  * To make use of this, specify the name of the source file as `pico_fsdata.inc` in `lwipopts.h`.