remove unused thread include

Threads are not natively used by the repository.  Remove all references
to `#include <thread>`.

Tested: Code still compiles and unit tests pass.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Iaff3915124e93adf7bb13566e0ff7cfe7576efd6
diff --git a/main.cpp b/main.cpp
index 7ade8e4..35dd59b 100644
--- a/main.cpp
+++ b/main.cpp
@@ -45,7 +45,6 @@
 #include <list>
 #include <map>
 #include <memory>
-#include <thread>
 #include <unordered_map>
 #include <utility>
 #include <vector>
diff --git a/pid/pidcontroller.cpp b/pid/pidcontroller.cpp
index 0a56057..c983c35 100644
--- a/pid/pidcontroller.cpp
+++ b/pid/pidcontroller.cpp
@@ -24,7 +24,6 @@
 #include <iostream>
 #include <map>
 #include <memory>
-#include <thread>
 #include <vector>
 
 namespace pid_control
diff --git a/pid/pidloop.cpp b/pid/pidloop.cpp
index 0ccf35c..888419b 100644
--- a/pid/pidloop.cpp
+++ b/pid/pidloop.cpp
@@ -27,7 +27,6 @@
 #include <map>
 #include <memory>
 #include <sstream>
-#include <thread>
 #include <vector>
 
 namespace pid_control
diff --git a/pid/stepwisecontroller.cpp b/pid/stepwisecontroller.cpp
index b93c349..2ed3d41 100644
--- a/pid/stepwisecontroller.cpp
+++ b/pid/stepwisecontroller.cpp
@@ -28,7 +28,6 @@
 #include <iostream>
 #include <map>
 #include <memory>
-#include <thread>
 #include <vector>
 
 namespace pid_control