qdoc: Removed text formatting from requisites table

Removed the teletype (code) formatting used in the requisite table:
include, qmake (qtvariable) and import statement (for QML types).

This makes the table look more uniform as it doesn't mix font
styles anymore.

Also, remove the closing </b> tag that caused incorrect html to
be generated.

Change-Id: I180a90c22d4b0066aade8ce38d13343076285ff0
Reviewed-by: Martin Smith <martin.smith@digia.com>