Refactor the handler function roff_block_sub() for clarity and simplicity.

Refactor the handler function roff_block_sub() for clarity and simplicity.

1. Do not needlessly access the function pointer table roffs[].
Instead, simply call the block closing function directly.

2. Sort code: handle both cases of block closing at the beginning
of the function rather than one at the beginning and one at the end.

3. Trim excessive, partially repetitive and obvious comments, also
making the comments considerably more precise.

No functional change.