Revert "[AMDGPU] Start documenting calling conventions. NFC"

This reverts commit aa7b127.

...because I really ought to install sphinx.

llvm/docs/AMDGPUUsage.rst

@@ -1064,67 +1064,6 @@ The AMDGPU backend supports the following LLVM IR attributes.
 
      ======================================= ==========================================================
 
-Calling Conventions
--------------------
-
-The AMDGPU backend supports the following calling conventions:
-
-  .. table:: AMDGPU Calling Conventions
-     :name: amdgpu-cc
-
-     =============================== ==========================================================
-     Calling Convention              Description
-     =============================== ==========================================================
-     ``ccc``                         The C calling convention. Used by default.
-                                     See :ref:`amdgpu-amdhsa-function-call-convention-non-kernel-functions`
-                                     for more details.
-
-     ``fastcc``                      The fast calling convention. Mostly the same as the ``ccc``.
-
-     ``coldcc``                      The cold calling convention. Mostly the same as the ``ccc``.
-
-     ``amdgpu_cs``                   Used for Mesa/AMDPAL compute shaders.
-                                     ..TODO::
-                                     Describe.
-
-     ``amdgpu_es``                   Used for AMDPAL shader stage before geometry shader if geometry is in
-                                     use. So either the domain (= tessellation evaluation) shader if
-                                     tessellation is in use, or otherwise the vertex shader.
-                                     ..TODO::
-                                     Describe.
-
-     ``amdgpu_gfx``                  Used for AMD graphics targets. Functions with this calling convention
-                                     cannot be used as entry points.
-                                     ..TODO::
-                                     Describe.
-
-     ``amdgpu_gs``                   Used for Mesa/AMDPAL geometry shaders.
-                                     ..TODO::
-                                     Describe.
-
-     ``amdgpu_hs``                   Used for Mesa/AMDPAL hull shaders (= tessellation control shaders).
-                                     ..TODO::
-                                     Describe.
-
-     ``amdgpu_kernel``               See :ref:`_amdgpu-amdhsa-function-call-convention-kernel-functions`
-
-     ``amdgpu_ls``                   Used for AMDPAL vertex shader if tessellation is in use.
-                                     ..TODO::
-                                     Describe.
-
-     ``amdgpu_ps``                   Used for Mesa/AMDPAL pixel shaders.
-                                     ..TODO::
-                                     Describe.
-
-     ``amdgpu_vs``                   Used for Mesa/AMDPAL last shader stage before rasterization (vertex
-                                     shader if tessellation and geometry are not in use, or otherwise
-                                     copy shader if one is needed).
-                                     ..TODO::
-                                     Describe.
-
-     =============================== ==========================================================
-
-
 .. _amdgpu-elf-code-object:
 
 ELF Code Object