refactor!: remove pcre2el package

BREAKING CHANGE: This removes the pcre2el package, which Doom was using
solely for one function to escape PCREs. In the interest of thinning out
Doom's core, I've hoisted a simpler version of the function into Doom's
stdlib so I can remove the dependency.

lisp/lib/strings.el

@@ -0,0 +1,15 @@
+;;; lisp/lib/strings.el -*- lexical-binding: t; -*-
+
+;;;###autoload
+(defun doom-pcre-quote (str)
+  "Like `reqexp-quote', but for PCREs."
+  (let ((special '(?. ?^ ?$ ?* ?+ ?? ?{ ?\\ ?\[ ?\| ?\())
+        (quoted nil))
+    (mapc (lambda (c)
+            (when (memq c special)
+              (push ?\\ quoted))
+            (push c quoted))
+          str)
+    (concat (nreverse quoted))))
+
+;;; end of strings.el

lisp/packages.el

@@ -31,7 +31,6 @@
 (package! better-jumper :pin "47622213783ece37d5337dc28d33b530540fc319")
 (package! dtrt-indent :pin "939c5e374ac0175bb7d561542e22e47a72d04aa8")
 (package! helpful :pin "4ba24cac9fb14d5fdc32582cd947572040e82b2c")
-(package! pcre2el :pin "380723b2701cceb75c266440fb8db918f3340d50")
 (package! smartparens :pin "f7cf316715e5018186c226aab8242c9e5ce131c8")
 (package! ws-butler :pin "e3a38d93e01014cd47bf5af4924459bd145fd7c4")