mail/msmtp: Remove use of symlink postinst/postrm

Avoid the postrm/postinst symlink addition and removal as
1) This fails to conflict with other packages which also provide
the same commands and makes what packages is supply the command
depend on which command was installed last.
2) Trunk devs don't like postrm/postinst symlink mangling
3) Packages changing things from other packages is considered bad
packaging pratice on most distros and debian, for example,
prohibits it.

Signed-off-by: Daniel Dickinson <lede@daniel.thecshore.com>

mail/msmtp/Makefile

@@ -112,19 +112,7 @@ define Package/msmtp/install
 		$(1)/etc/msmtprc
 	$(INSTALL_DIR) $(1)/usr/bin
 	$(CP) $(PKG_INSTALL_DIR)/usr/bin/msmtp $(1)/usr/bin/
-endef
-
-define Package/msmtp/postinst
-	[ -e $${IPKG_INSTROOT}/usr/sbin/sendmail ] || {
-		mkdir -p $${IPKG_INSTROOT}/usr/sbin
-		ln -sf ../bin/msmtp $${IPKG_INSTROOT}/usr/sbin/sendmail
-	}
-endef
-
-define Package/msmtp/prerm
-	[ "../bin/msmtp" = "$(readlink -qs $${IPKG_INSTROOT}/usr/sbin/sendmail)" ] && {
-		rm -f $${IPKG_INSTROOT}/usr/sbin/sendmail
-	}
+	ln -s ../bin/msmtp $(1)/usr/sbin/sendmail
 endef
 
 Package/msmtp-nossl/conffiles = $(Package/msmtp/conffiles)