Eliminate mi_run_to_main, introduce mi_clean_restart

Since we now have mi_runto_main which is like runto_main, eliminate
mi_run_to_main, in favor of a new MI clean_restart counterpart --
mi_clean_restart -- and mi_runto_main.

This makes MI testcases look a bit more like CLI testcases.

gdb/testsuite/ChangeLog:

	* lib/mi-support.exp (mi_clean_restart): New.
	(mi_run_to_main): Delete.
	All callers adjust to use mi_clean_restart / mi_runto_main.

Change-Id: I34920bab4fea1f23fb752928c2969c1f6ad714b6

gdb/testsuite/gdb.python/py-mi-events.exp

@@ -49,7 +49,8 @@ if [is_remote host] {
 }
 
 mi_gdb_test "-file-exec-and-symbols ${filename}"  ".*\\^done" "file-exec-and-symbols operation"
-mi_run_to_main
+mi_gdb_load ${binfile}
+mi_runto_main
 
 
 # register the python event handlers with test-events command

gdb/testsuite/gdb.python/py-mi-var-info-path-expression.exp

@@ -18,11 +18,6 @@
 load_lib mi-support.exp
 set MIFLAGS "-i=mi"
 
-gdb_exit
-if {[mi_gdb_start]} {
-    continue
-}
-
 #
 # Start here
 #
@@ -32,6 +27,8 @@ if {[gdb_compile "$srcdir/$subdir/$srcfile" $binfile executable {debug}] != "" }
     return -1
 }
 
+mi_clean_restart $binfile
+
 # Skip all tests if Python scripting is not enabled.
 if { [mi_skip_python_tests] } { continue }
 
@@ -48,9 +45,7 @@ mi_gdb_test "set python print-stack full" \
   ".*\\^done" \
   "set python print-stack full"
 
-
-mi_run_to_main
-
+mi_runto_main
 
 mi_continue_to_line [gdb_get_line_number "next line" ${srcfile}] \
   "step to breakpoint"