py/mkenv.mk: Remove -s and -S args from PYTHON variable.

Qstr auto-generation is now much faster so this optimisation for start-up
time is no longer needed.  And passing "-s -S" breaks some things, like
stmhal's "make deploy".

py/mkenv.mk

@@ -42,7 +42,7 @@ ECHO = @echo
 CP = cp
 MKDIR = mkdir
 SED = sed
-PYTHON = python -s -S
+PYTHON = python
 
 AS = $(CROSS_COMPILE)as
 CC = $(CROSS_COMPILE)gcc