scanner: remove pos 0 hack which is no longer needed (#10935)

vlib/v/scanner/scanner.v

@@ -688,11 +688,6 @@ fn (mut s Scanner) text_scan() token.Token {
 				s.is_inter_end = true
 				s.is_inter_start = false
 			}
-			if s.pos == 0 && next_char == ` ` {
-				// If a single letter name at the start of the file, increment
-				// Otherwise the scanner would be stuck at s.pos = 0
-				s.pos++
-			}
 			return s.new_token(.name, name, name.len)
 		} else if c.is_digit() || (c == `.` && nextc.is_digit()) {
 			// `123`, `.123`

vlib/v/scanner/tests/position_0_err.out

@@ -0,0 +1,5 @@
+vlib/v/scanner/tests/position_0_err.vv:1:1: error: unused variable: `i`
+    1 | i := 'hello'
+      | ^
+    2 | x := 3
+    3 | y := 2

vlib/v/scanner/tests/position_0_err.vv

@@ -0,0 +1,4 @@
+i := 'hello'
+x := 3
+y := 2
+println(x + y)

vlib/v/tests/valgrind/simple_interpolation_script_mode.v

@@ -1,5 +1,4 @@
+// TODO: @medvednikov: autofree on script mode does not work when first variable is on position 0 due to the code in `cgen.v:1115`
 v := 't'
-
 s := '${v}.tmp'
-
 println(s)