mockftpserver: drop .classpath files and update README.txt

Android build does not use the .classpath files, but they contain
references to log4j which may show up in security audits.

Update README.txt since it's possible to use mockftpserver without
log4j.

Bug: 210115136
Test: m
Change-Id: Iff60241aec3b9fa685969e18f41c48e87165c396
22 files changed