Revert SplitContainer minimum size splitting changes (#64676 and #64800)

This reverts commits 185b1a5bd333c5e75da5219e66cb759b5e6c3684 and 19ad31b89fc293cbd3c826b4dab6140b65895121.

The original PR and its fixup still had regressions, so we're going back
to the drawing board to reattempt fixing #43749.

Fixes #64785.
Fixes #64851.
Fixes #64866.

scene/gui/split_container.cpp

@@ -97,16 +97,12 @@ void SplitContainer::_resort() {
 
 	// Compute the final middle separation.
 	middle_sep = no_offset_middle_sep;
-	if (prev_no_offset_middle_sep != INT_MAX) {
-		split_offset -= middle_sep - prev_no_offset_middle_sep;
-	}
-	prev_no_offset_middle_sep = middle_sep;
-
 	if (!collapsed) {
 		int clamped_split_offset = CLAMP(split_offset, ms_first[axis] - no_offset_middle_sep, (get_size()[axis] - ms_second[axis] - sep) - no_offset_middle_sep);
 		middle_sep += clamped_split_offset;
 		if (should_clamp_split_offset) {
 			split_offset = clamped_split_offset;
+
 			should_clamp_split_offset = false;
 		}
 	}

scene/gui/split_container.h

@@ -47,7 +47,6 @@ private:
 	bool should_clamp_split_offset = false;
 	int split_offset = 0;
 	int middle_sep = 0;
-	int prev_no_offset_middle_sep = INT_MAX;
 	bool vertical = false;
 	bool dragging = false;
 	int drag_from = 0;