Remove i8x16.mul

Consensus for the removal is documented in WebAssembly#28 and
WebAssembly#98.

Author: penzn

proposals/simd/BinarySIMD.md

@@ -109,7 +109,6 @@ The `v8x16.shuffle` instruction has 16 bytes after `simdop`.
 | `i8x16.sub`                |    `0x5a`| -                  |
 | `i8x16.sub_saturate_s`     |    `0x5b`| -                  |
 | `i8x16.sub_saturate_u`     |    `0x5c`| -                  |
-| `i8x16.mul`                |    `0x5d`| -                  |
 | `i16x8.neg`                |    `0x62`| -                  |
 | `i16x8.any_true`           |    `0x63`| -                  |
 | `i16x8.all_true`           |    `0x64`| -                  |

proposals/simd/ImplementationStatus.md

@@ -86,7 +86,6 @@
 | `i8x16.sub`                |               `-msimd128` | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
 | `i8x16.sub_saturate_s`     |               `-msimd128` | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
 | `i8x16.sub_saturate_u`     |               `-msimd128` | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
-| `i8x16.mul`                |               `-msimd128` | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
 | `i16x8.neg`                |               `-msimd128` | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
 | `i16x8.any_true`           |               `-msimd128` | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
 | `i16x8.all_true`           |               `-msimd128` | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |

proposals/simd/SIMD.md

@@ -367,7 +367,6 @@ def S.sub(a, b):
 ```
 
 ### Integer multiplication
-* `i8x16.mul(a: v128, b: v128) -> v128`
 * `i16x8.mul(a: v128, b: v128) -> v128`
 * `i32x4.mul(a: v128, b: v128) -> v128`