[mlir][spirv][doc] Remove duplicate syntax formats (#73386)

Some operations defined their syntax both in the documentation and via
`assemblyFormat`. This leads to two syntax descriptions in the
documentation for SPIR-V, see for example the documentation for
[`spirv.mlir.yield`](https://mlir.llvm.org/docs/Dialects/SPIR-V/#spirvmliryield-spirvyieldop).
Since the `assemblyFormat` is used to generate the actual parsers and
printer implementations, this PR removes the manual syntax descriptions.
(Similar to https://github.com/llvm/llvm-project/pull/73343.)

The strategy that I used to find the duplicates was pretty
uncomplicated. I scrolled through the [SPIR-V
Dialect](https://mlir.llvm.org/docs/Dialects/SPIR-V) to find all
duplicates and then remove the duplicate text from the `td` file.

Note that the `Syntax:` block in the docs is a good proxy for whether
`assemblyFormat` is defined because it will only be generated if the op
has defined `assemblyFormat` (`op.hasAssemblyFormat()`):


https://github.com/llvm/llvm-project/blob/e970652776bd07dbe42be557bf98722749230653/mlir/tools/mlir-tblgen/OpDocGen.cpp#L108-L124


https://github.com/llvm/llvm-project/blob/e970652776bd07dbe42be557bf98722749230653/mlir/tools/mlir-tblgen/OpDocGen.cpp#L197-L199

Related issue https://github.com/llvm/llvm-project/issues/73359.