drop support for win32/osx and checkupdate plugin

that plugin has never been built in linux anyway due to logic
in configure.ac

plugins/externaltools/data/Makefile.am

@@ -2,31 +2,14 @@ TOOL_MERGE=$(top_srcdir)/plugins/externaltools/scripts/pluma-tool-merge.pl
 
 tools_in_files = \
 	build.tool.in \
-	remove-trailing-spaces.tool.in
-
-tools_in_linux = \
 	open-terminal-here.tool.in \
+	remove-trailing-spaces.tool.in \
 	run-command.tool.in \
 	search-recursive.tool.in \
 	switch-c.tool.in
 
-tools_in_osx = \
-	open-terminal-here-osx.tool.in
-
-tools_in_win32 =
-
 install_tools_in_files = $(tools_in_files)
 
-if PLATFORM_OSX
-install_tools_in_files += $(tools_in_osx)
-else
-if PLATFORM_WIN32
-install_tools_in_files += $(tools_in_win32)
-else
-install_tools_in_files += $(tools_in_linux)
-endif
-endif
-
 desktop_in_files = $(install_tools_in_files:.tool.in=.desktop.in)
 desktop_files    = $(install_tools_in_files:.tool.in=.desktop)
 
@@ -34,10 +17,7 @@ tools_SCRIPTS = $(install_tools_in_files:.tool.in=)
 toolsdir = $(PLUMA_PLUGINS_DATA_DIR)/externaltools/tools
 
 all_tools_in_files = \
-	$(tools_in_files) \
-	$(tools_in_linux) \
-	$(tools_in_osx) \
-	$(tools_in_win32)
+	$(tools_in_files)
 
 all_desktop_in_files = $(all_tools_in_files:.tool.in=.desktop.in)
 all_desktop_files = $(all_tools_in_files:.tool.in=.desktop)
@@ -63,5 +43,4 @@ DISTCLEANFILES = \
 	$(all_desktop_files) \
 	$(all_tools_files)
 
-
 -include $(top_srcdir)/git.mk

plugins/externaltools/data/open-terminal-here-osx.desktop.in

@@ -1,8 +0,0 @@
-[Pluma Tool]
-_Name=Open terminal here
-_Comment=Open a terminal in the document location
-Input=nothing
-Output=output-panel
-Applicability=local
-Save-files=nothing
-Languages=

plugins/externaltools/data/open-terminal-here-osx.tool.in

@@ -1,16 +0,0 @@
-#!/usr/bin/osascript
-
-set the_path to system attribute "PLUMA_CURRENT_DOCUMENT_DIR"
-set cmd to "cd " & quoted form of the_path
-
-tell application "System Events" to set terminalIsRunning to exists application process "Terminal"
-
-tell application "Terminal"
-	activate
-	
-	if terminalIsRunning is true then
-		do script with command cmd
-	else
-		do script with command cmd in window 1
-	end if
-end tell