remove unused iota2 functionality

Some of iota2 functionality seems to be unused but still maintain. They increase the complexity of the code and its maintainability. The purpose of this issue is to list functionalities that can be remove from iota2 source code. However, any functionality removed will have to be replaced by an additional tool (provided by iota2) and specific documentation.

functionality name	tool	status (still available/remove in progress/removed)
auto-context	-	removed MR !140 (merged)
coregistration	-	removed MR !139 (merged)
crop-mix	launch iota2 multiple times	removed MR !143 (merged)
S1-S2 post classification fusion	launch iota2 multiple times.	removed MR !142 (merged)
dimensionality reduction	- ? or use it through 'external features' worflow	removed MR !141 (closed)

for "S1-S2 post classification fusion" the futur tool will be a interesting feature because it will generalize the post classification fusion to any sensors.