sysutils/*exfat*: update to 1.2.4

• Chase project move to GitHub
• Chase patent licensing URL [1]
• Restore GPLv2 after r328060 [2]
• Fix build on DragonFly
• Drop unused iconv dependency

PR: 199874, 210823
PR: 210162 [1]
Suggested by: decke, tijl [2] (via bug 193629)
Approved by: maintainer timeout (2 weeks)
MFH: 2016Q3