Revert "Enable significant indentation after return"

A `return` is not necessarily followed by anything. So our general principles
indicate that indentation should not be significant after it, since otherwise
an off-by-one-space error could change meaning.

Author: odersky

compiler/src/dotty/tools/dotc/parsing/Tokens.scala

@@ -270,7 +270,7 @@ object Tokens extends TokensCommon {
   final val closingRegionTokens = BitSet(RBRACE, CASE) | statCtdTokens
 
   final val canStartIndentTokens: BitSet =
-    statCtdTokens | BitSet(COLONEOL, EQUALS, ARROW, LARROW, WHILE, TRY, FOR, RETURN, IF, WITH)
+    statCtdTokens | BitSet(COLONEOL, EQUALS, ARROW, LARROW, WHILE, TRY, FOR, IF, WITH)
       // `if` is excluded because it often comes after `else` which makes for awkward indentation rules  TODO: try to do without the exception
 
   /** Faced with the choice between a type and a formal parameter, the following

docs/docs/reference/other-new-features/indentation.md

@@ -28,7 +28,7 @@ There are two rules:
        class, object, given, or enum definition, in an enum case, or after a package clause, or
      - after one of the following tokens:
     ```
-    =  =>  <-  if  then  else  while  do  try  catch  finally  for  yield  match  return
+    =  =>  <-  if  then  else  while  do  try  catch  finally  for  yield  match
     ```
     If an `<indent>` is inserted, the indentation width of the token on the next line
     is pushed onto `IW`, which makes it the new current indentation width.