Renames GraduationHat icon to Cap (#2139)

* rename grad hat icon

* changeset

* rm file

Author: bruugey

.changeset/shiny-experts-prove.md

@@ -2,4 +2,4 @@
 '@leafygreen-ui/icon': minor
 ---
 
-Adds GraduationHat icon to glyph set
+Adds `'Cap'` icon to glyph set