Never render "Show More Context" inside an inline comment suggestion diff

Summary:
See PHI1896. If you do this:

• Create an inline comment over a wide range of lines.
• Suggest an edit.
• Make a change near the beginning of the block.
• Make a change near the end of the block.
• Save the inline.

...you get a rendering which includes a "Show More Context" fold in the middle.

Currently, this element renders in a visually broken way and consumes too many columns.

However, this element isn't ever desirable inside inline comment suggestions. Stop it from rendering entirely.

Test Plan:

• Made an inline comment suggestion across lines 1-50 with edits at the beginning and end, saw a contiguous diff.
• Made smaller inline comment suggestions (one line, a few lines).

Differential Revision: https://secure.phabricator.com/D21476