Fix up support for Mavlink All dialect

QGCExternalLibs.pri

@@ -55,6 +55,7 @@ isEmpty(MAVLINK_CONF) {
         message($$sprintf("Using user-supplied mavlink dialect '%1' specified in user_config.pri", $$MAVLINK_CONF))
     } else {
         MAVLINK_CONF = all
+        message($$sprintf("Using MAVLink dialect '%1'.", $$MAVLINK_CONF))
     }
 }
 
@@ -67,17 +68,9 @@ contains (CONFIG, QGC_DISABLE_APM_MAVLINK) {
     CONFIG  += ArdupilotEnabled
 }
 
-# First we select the dialect, checking for valid user selection
-# Users can override all other settings by specifying MAVLINK_CONF as an argument to qmake
-!isEmpty(MAVLINK_CONF) {
-    message($$sprintf("Using MAVLink dialect '%1'.", $$MAVLINK_CONF))
-}
-
 # Then we add the proper include paths dependent on the dialect.
 INCLUDEPATH += $$MAVLINKPATH
 
-exists($$MAVLINKPATH/common) {
-    !isEmpty(MAVLINK_CONF) {
 count(MAVLINK_CONF, 1) {
     exists($$MAVLINKPATH/$$MAVLINK_CONF) {
         INCLUDEPATH += $$MAVLINKPATH/$$MAVLINK_CONF
@@ -88,12 +81,6 @@ exists($$MAVLINKPATH/common) {
 } else {
     error(Only a single mavlink dialect can be specified in MAVLINK_CONF)
 }
-    } else {
-        INCLUDEPATH += $$MAVLINKPATH/common
-    }
-} else {
-    error($$sprintf("MAVLink folder does not exist at '%1'! Run 'git submodule init && git submodule update' on the command line.",$$MAVLINKPATH_REL))
-}
 
 #
 # [REQUIRED] EIGEN matrix library

custom-example/custom.pri

@@ -23,7 +23,6 @@ DEFINES += APP_VERSION_STR=\"\\\"$$CUSTOM_QGC_VERSION\\\"\"
 message(Custom QGC Version: $${CUSTOM_QGC_VERSION})
 
 # Build a single flight stack by disabling APM support
-MAVLINK_CONF = common
 CONFIG  += QGC_DISABLE_APM_MAVLINK
 CONFIG  += QGC_DISABLE_APM_PLUGIN QGC_DISABLE_APM_PLUGIN_FACTORY