Bug 1037211 - Remove redundant --enable-content-sandbox-reporter.

It's enabled by default on B2G as of bug 979590, so this shouldn't
change anything.
Merge pull request #178 from jld/bug1037211

Bug 1037211 - Remove redundant --enable-content-sandbox-reporter. r=kang
Bug 1029533 - Add libmtp.so to libraries needed to build libxul.so