tla-mode: Let indent-line-to decide on (point) location

This is similar to

     fc1af6d "Let `indent-line-to` decide on (point) location"

It turns out there's two indenation functions, so fix the 2nd one as well.

This unbreaks (newline-and-indent).

Before this commit calling newline-and-indent would put caret at the
beginning of line. This is not what a user wants, because they usually
desire continue typing code on the new line.

So remove the save-excursion call.

While at it, remove the beginning-of-line call as well, because both
are called first thing inside (pcal-mode--indent-column), so as far as
that function concerned having them earlier is unnecessary.

tla-pcal-mode.el

@@ -176,11 +176,8 @@
 (defun tla-mode-indent-line ()
   "Indent the current line according to TLA+ rules."
   (interactive)
-  (save-excursion
-    (beginning-of-line)
-    (let ((col (tla-mode--indent-column)))
-      (when col
-        (indent-line-to col)))))
+  (when-let ((col (tla-mode--indent-column)))
+    (indent-line-to col)))
 
 (defcustom pcal-mode-indent-offset 2
   "Amount of columns to indent lines in PlusCal code."