Revert "transform/EmitVertexPointSize: Handle entry point parameters"

This reverts commit 05e16ed1c5.

Reason for revert: Breaks Dawn autoroll.

 [ RUN      ] VertexBufferRobustnessTest.DetectInvalidValues/Metal_Intel_R_UHD_Graphics_630__e_metal_enable_vertex_pulling
 ../../src/tests/DawnTest.cpp:945: Failure
 Value of: self->mExpectError
   Actual: false
 Expected: true
 Got unexpected device error: Tint SPIRV reader failure:
 Parser: error: cannot store a value other than constant 1.0 to PointSize builtin: OpStore %8 %18


Original change's description:
> transform/EmitVertexPointSize: Handle entry point parameters
>
> Generate a new struct that contains members of the original return
> type with the point size appended to it, and replace return statements
> as necessary.
>
> Fixed: tint:732
> Change-Id: I2b5816144d5e95c65baca95dc0c50b4dfdd25ed3
> Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/48980
> Auto-Submit: James Price <jrprice@google.com>
> Commit-Queue: James Price <jrprice@google.com>
> Reviewed-by: Ben Clayton <bclayton@google.com>

TBR=bclayton@google.com,jrprice@google.com,noreply+kokoro@google.com

Change-Id: Id795d5320471d09d66a964c8e469b60da8f0a672
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/49260
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>

src/program_builder.h

@@ -700,9 +700,6 @@ class ProgramBuilder {
   // AST helper methods
   //////////////////////////////////////////////////////////////////////////////
 
-  /// @return a new unnamed symbol
-  Symbol Sym() { return Symbols().New(); }
-
   /// @param name the symbol string
   /// @return a Symbol with the given name
   Symbol Sym(const std::string& name) { return Symbols().Register(name); }