Updated movgrab to 1.2.1

The old package was pretty outdated. This installs the latest version
of movgrab. For the sake of simplicity and because case-insensitivity is
a thing, there's a call on the formula that removes the INSTALL file
before running make install. This is to avoid the old 'install is up to
date' message. Also removed an old workaround for compiling libUseful,
as it is no longer necessary.