Fix unnecessary nesting of `meta.block.c`

[winstliu]

This is pretty ridiculous. For example, try logging the scopes of this line. I get:

• source.c
  • meta.function.c
    • meta.block.c
      • meta.block.c
        • meta.block.c
          • keyword.control.c

And this is the list of scopes in a file I'm currently working with that's heavily based off of language-c:

• source.sp
  • meta.function.sp
    • meta.block.sp
      • meta.block.sp
        • meta.block.sp
          • meta.block.sp
            • meta.block.sp
              • meta.block.sp
                • meta.block.sp
                  • meta.block.sp

(there's actually eleven meta.blocks; GFM just can't render past 8 of them)
language-java handles this pretty well; we should look there for inspiration.