[pseudo] remove most of clang-pseudo

This was never completed, in particular we still wanted:

- disambiguation all grammatical ambiguity, e.g. by cross-referencing
  reused identifiers
- heuristic symbol resolution
- conversion to syntax trees

The parts still used by clangd remain and will be dealt with later.

See https://discourse.llvm.org/t/removing-pseudo-parser/71131/5
Original design doc: https://docs.google.com/document/d/1eGkTOsFja63wsv8v0vd5JdoTonj-NlN3ujGF0T7xDbM/edit

Author: sam-mccall

clang-tools-extra/pseudo/CMakeLists.txt

@@ -1,11 +1,5 @@
 include_directories(include)
-include_directories(${CMAKE_CURRENT_BINARY_DIR}/include)
-add_subdirectory(include)
-add_subdirectory(gen)
 add_subdirectory(lib)
-add_subdirectory(tool)
-add_subdirectory(fuzzer)
-add_subdirectory(benchmarks)
 if(CLANG_INCLUDE_TESTS)
   add_subdirectory(unittests)
   add_subdirectory(test)

clang-tools-extra/pseudo/README.md

@@ -1,3 +1,10 @@
+# Removed
+
+This was never completed and most of the implementation has been removed.
+This document remains for historical interest, for now.
+
+See https://docs.google.com/document/d/1eGkTOsFja63wsv8v0vd5JdoTonj-NlN3ujGF0T7xDbM/edit
+
 # clang pseudoparser
 
 This directory implements an approximate heuristic parser for C++, based on the