devel/nspr: cleanup cruft to improve style

• Remove out-of-tree build (in favor of D4157)
• Remove custom do-install (config/nsinstall works fine) [1]
• Convert to new testing framework
• Refresh patches with |make makepatch| but leave damage out [2]

[1] Requires PORTREVISION per new entry in plist and DEBUG builds

no longer embedding WRKDIR in source file name

[2] Here's a list with * indicating severity:

• • • Lost original ptthread.c hunk from patch-bug301986
    • Mixed patch-bug782111 into patch-bug301986
  • Duplicated context lines
• Wrong timestamps with USES=pathfix