Delete dead code

The quick-lint-js-generate-error-documentation tool is no longer used.
Delete it.

Subsequently, the md4c third-party library is no longer used. Delete it.

Author: strager

docs/CMakeLists.txt

@@ -4,31 +4,6 @@
 cmake_minimum_required(VERSION 3.10)
 include(GNUInstallDirs)
 
-add_executable(
-  quick-lint-js-generate-error-docs
-  generate-error-docs.cpp
-)
-target_link_libraries(
-  quick-lint-js-generate-error-docs
-  PRIVATE
-  md4c
-  quick-lint-js-docs-lib
-  quick-lint-js-lib
-)
-
-add_library(
-  quick-lint-js-docs-lib
-  error-documentation.cpp
-)
-target_include_directories(quick-lint-js-docs-lib PUBLIC .)
-target_link_libraries(
-  quick-lint-js-docs-lib
-  PUBLIC
-  quick-lint-js-lib
-  PRIVATE
-  md4c
-)
-
 install(
   FILES quick-lint-js.1
   DESTINATION "${CMAKE_INSTALL_MANDIR}/man1"