Fix precompile warnings in Julia 1.12 (#559)

Remove unused type parameters in methods.

Before:
```julia
(@v1.12) pkg> precompile
Precompiling packages finished.
  38 dependencies successfully precompiled in 36 seconds. 704 already precompiled.
  1 dependency had output during precompilation:
┌ LoopVectorization → ForwardDiffNNlibExt
│  WARNING: method definition for relu at /home/hp74lr/.julia/dev/LoopVectorization/ext/ForwardDiffNNlibExt.jl:5 declares type variable S but does not use it.
│  WARNING: method definition for leakyrelu at /home/hp74lr/.julia/dev/LoopVectorization/ext/ForwardDiffNNlibExt.jl:22 declares type variable S but does not use it.
└ 
```

After:
```julia
(@v1.12) pkg> precompile
Precompiling packages finished.
  37 dependencies successfully precompiled in 34 seconds. 705 already precompiled.
```

Author: PatrickHaecker

ext/ForwardDiffNNlibExt.jl

@@ -4,7 +4,7 @@ using LoopVectorization, VectorizationBase, SLEEFPirates, ForwardDiff, NNlib
 
 @generated function NNlib.relu(
   x::ForwardDiff.Dual{T,<:LoopVectorization.AbstractSIMD,N}
-) where {T,S,N}
+) where {T,N}
   quote
     $(Expr(:meta, :inline))
     v = x.value
@@ -22,7 +22,7 @@ end
 @generated function NNlib.leakyrelu(
   x::ForwardDiff.Dual{T,<:LoopVectorization.AbstractSIMD,N},
   a = 0.01
-) where {T,S,N}
+) where {T,N}
   quote
     $(Expr(:meta, :inline))
     v = x.value