Remove docs/release section from the Bio-Formats repository

The download page generation is maintained under a separate
openmicroscopy/ome-release repository so this folder is not needed anymore.
Remove docs/release from the Travis build job
merge dev_5_0 -D org -I include -E exclude: PR 856 (Initial version of bfCheckJavaMemory)
merge dev_5_0 -D org -I include -E exclude: PR 860 (UpgradeChecker: fix the stable version number)
merge dev_5_0 -D org -I include -E exclude: PR 862 (Permit cppwrap failure (rebased onto dev_5_0))
merge dev_5_0 -D org -I include -E exclude: PR 863 (Remove docs/release section from the Bio-Formats repository)