Drop pointless use of CannotInstallFormulaError

These are not caught anywhere, just raise the string. Missed in
1b3b61ff08a4ee5979838f7dbc171e9b38e83f7c.
cabal-install: update 1.20.0.3_1 bottle.
libestr: update 0.1.9 bottle.
libetonyek: update 0.1.1 bottle.
libftdi: update 1.1 bottle.
libgaiagraphics: update 0.5 bottle.
libgda: add 5.2.0_1 bottle.
libgee: update 0.16.0 bottle.
libicns: update 0.8.1_1 bottle.
libident: update 0.32 bottle.
libidl: update 0.8.14 bottle.
libltc: update 1.1.4 bottle.
liblwgeom: update 2.1.1 bottle.
libmaa: update 1.3.2 bottle.
libmatroska: update 1.4.1 bottle.
libmicrohttpd: update 0.9.37 bottle.
libmikmod: update 3.3.7 bottle.
libmms: update 0.6.4 bottle.
libmonome: update 1.2 bottle.
libmp3splt: update 0.8.2 bottle.