Revert commits from d30691 to c04d4c

since ROOT stopped compiling.

Revert "Remove dead code I know I can remove"

This reverts commit c04d4cf6.

Revert "[Math/Fit] Update documentation"

This reverts commit 76f58d3a.

Revert "Merge old PoissonLogL functions into new interfaces"

This reverts commit b1cd6e68.

Revert "Merge old LogL functions into new interfaces"

This reverts commit 059092a7.

Revert "Merge old functions into new interfaces"

This reverts commit ccecadaf.

Revert "Move template specification definitions to source file"

This reverts commit 5192cf5b.

Revert "Fix undefined default initialization"

This reverts commit 92af804e.

Revert "Fix bug in gradient evaluation"

This reverts commit cbc475ca.

Revert "Apply clang-format"

This reverts commit 7007245d.

Revert "Improve loop performance"

This reverts commit 9ddf280f.

Revert "Fix iterator type"

This reverts commit 271738b8.

Revert "Fix non initialization warning"

This reverts commit 5b576e20.

Revert "Discard unnecessary operations"

This reverts commit 2dd87289.

Revert "Add braces for consistency"

This reverts commit dcc37acf.

Revert "Update infinite check functions"

This reverts commit 06c127da.

Revert "Remove unnecessary specialization"

This reverts commit 7e767e98.

Revert "Remove unnecessary cast"

This reverts commit c8020a0f.

Revert "Fix comment"

This reverts commit 711185dc.

Revert "Add missing include"

This reverts commit d6bfc08a.

Revert "Factor out objective functions from FitUtil"

This reverts commit c498e8c8.

Revert "Fix header comment"

This reverts commit d30691e4.