Remove repeated initial entry in fitlog

[palday]

if you set thin = 1 it is

julia> ds = MixedModels.dataset(:dyestuff)
Arrow.Table with 30 rows, 2 columns, and schema:
 :batch  String
 :yield  Int16

julia> contrasts = Dict{Symbol, AbstractContrasts}(:batch => Grouping())
Dict{Symbol, AbstractContrasts} with 1 entry:
  :batch => Grouping()

julia> thin = 1
1

julia> dsm01 = let
           form = @formula yield ~ 1 + (1|batch)
           fit(MixedModel, form, ds; contrasts, thin)
       end
Linear mixed model fit by maximum likelihood
 yield ~ 1 + (1 | batch)
   logLik   -2 logLik     AIC       AICc        BIC    
  -163.6635   327.3271   333.3271   334.2501   337.5307

Variance components:
            Column    Variance Std.Dev.
batch    (Intercept)  1388.3332 37.2603
Residual              2451.2501 49.5101
 Number of obs: 30; levels of grouping factors: 6

  Fixed-effects parameters:
────────────────────────────────────────────────
              Coef.  Std. Error      z  Pr(>|z|)
────────────────────────────────────────────────
(Intercept)  1527.5     17.6946  86.33    <1e-99
────────────────────────────────────────────────

julia> first(dsm01.optsum.fitlog, 3)
3-element Vector{Tuple{Vector{Float64}, Float64}}:
 ([1.0], 327.76702162461663)
 ([1.0], 327.76702162461663)
 ([1.75], 331.03619322245146)

Originally posted by @dmbates in #615 (comment)

Note that this doesn't occur when calling refit! as currently done in the tests.