[css-backgrounds-3]/[css-box-3]/[css-speech-1] drop parens around "see individual properties"

[keithamus]

In css-backgrounds-3/css-box-3 the Initial: and Computed value: properties use (see individual properties) (note the parens). In css-speech-1 it uses N/A (see individual properties). Both of these seem inconsistent with the overwhelming style of see computed properties (no N/A, no parens). This PR drops the parens around the term to make it more consistent. The N/A seems redundant in css-speech-1 as it's not "not applicable", it is applicable, the application being that the individual properties should be consulted. Of course I am happy to take guidance here if we feel as if N/A (see individual properties) should be kept, but it seems to be the only instance across all the specs is within css-speech-1.