fix(fish): remove FORGIT variable

We set a `git-forgit` alias later, so this variable is not needed
anymore.

Author: folliehiyuki

conf.d/forgit.plugin.fish

@@ -2,10 +2,8 @@
 
 set INSTALL_DIR (dirname (dirname (status -f)))
 set -x FORGIT_INSTALL_DIR "$INSTALL_DIR/conf.d"
-set -x FORGIT "$FORGIT_INSTALL_DIR/bin/git-forgit"
-if [ ! -e "$FORGIT" ]
+if [ ! -e "$FORGIT_INSTALL_DIR/bin/git-forgit" ]
     set -x FORGIT_INSTALL_DIR "$INSTALL_DIR/vendor_conf.d"
-    set -x FORGIT "$FORGIT_INSTALL_DIR/bin/git-forgit"
 end
 
 function forgit::warn