api/pom.xml: Add javax.xml.bind.annotation.adapters to Import-Package.

This patch fixes a bug that XmlJavaTypeAdapter might not be visible to
Jackson.

Other changes:

  * Remove unnecessary dependencies in pom.xml.

Change-Id: Ic5efede7d8d444e5248856379cd168b0967bf499
Signed-off-by: Shigeru Yasuda <s-yasuda@da.jp.nec.com>