Use system hunspell

Stop building texmaker's own, utdated bundled copy of hunspell. In addition to
the obvious reasons, this is necessary to get the port to build with the
upcoming Qt 5.6, as it passes -std=gnu++11 to the compiler automatically when
it's supported and building the bundled hunspell failed like this:

hunspell/affentry.hxx:28:94: error: cannot initialize a parameter of type 'unsigned short' with an rvalue of type 'nullptr_t'
hunspell/affentry.hxx:91:103: error: cannot initialize a parameter of type 'unsigned short' with an rvalue of type 'nullptr_t'

See also: https://www.freebsd.org/doc/en/books/porters-handbook/bundled-libs.html

PR: 212366
Approved by: portmgr (mat)