Fix for brackets lost in merge.
Removed unused force arguments for angular bending springs and avoid
redundant calculation for counterforces.
Merge branch 'hair_immediate_fixes' into hair_system_solver
Removed block matrix indices storage from ClothSpring struct.

This is not necessary: the implicit solver data can keep track instead
of how many off-diagonal matrix blocks are in use (provided the
allocation limit is calculated correctly). Every time a spring is
created it then simply increments this counter and uses the block index
locally - no need to store this persistently.
Removed block matrix indices storage from ClothSpring struct.

This is not necessary: the implicit solver data can keep track instead
of how many off-diagonal matrix blocks are in use (provided the
allocation limit is calculated correctly). Every time a spring is
created it then simply increments this counter and uses the block index
locally - no need to store this persistently.
Merge branch 'hair_immediate_fixes' into hair_system_solver
Stretch spring force for the new hair solver data.