Optimize out local_size_N=1 in comp shader's layout()

Input:
```glsl
layout(local_size_x=256, local_size_y=1, local_size_z=1) in;
void main() {}
```
Output:
```glsl
layout(local_size_x=256,local_size_y=1,local_size_z=1)in;void main(){}
```
Expected output:
```glsl
layout(local_size_x=256)in;void main(){}
```