Remove purescript-str module

This file is another legacy from Haskell-mode. It contains no
autoloaded or interactive (i.e. ones somebody could bind to a hotkey)
functions, and the module isn't used anywhere in the code. Some of the
functions are specific to Haskell — for example, `purescript-str-trim`
mentions some "PureScript Report", which actually refers to Haskell
report (when the mode was imported from Haskell, code was
batch-renamed from haskell to purescript). So there's no point to prefer
purescript-str-trim to plain string-trim.

Thus, let's just remove the module from the codebase.

Author: Hi-Angel

Makefile

@@ -19,7 +19,6 @@ ELFILES = \
 	purescript-presentation-mode.el \
 	purescript-simple-indent.el \
 	purescript-sort-imports.el \
-	purescript-str.el \
 	purescript-unicode-input-method.el \
 	purescript-utils.el \
 	purescript-decl-scan.el \
@@ -28,7 +27,6 @@ ELFILES = \
 	tests/purescript-sort-imports-tests.el \
 	tests/purescript-indentation-tests.el \
 	tests/purescript-font-lock-tests.el \
-	tests/purescript-str-tests.el
 
 ELCFILES = $(ELFILES:.el=.elc)
 AUTOLOADS = purescript-mode-autoloads.el
@@ -48,7 +46,6 @@ compile: $(ELCFILES)
 
 test: compile
 	@$(BATCH) -l tests/purescript-sort-imports-tests.elc \
-		-l tests/purescript-str-tests.elc \
 		-l tests/purescript-indentation-tests.elc \
 		-l tests/purescript-font-lock-tests.elc \
 		-f ert-run-tests-batch-and-exit