Simpler Python requirements check (#11939)

Don't require the full requirements.txt
If we do that we are likely to send users back to the python2 support branch when new dependencies arise.

scripts/check_requirements.py

@@ -9,21 +9,18 @@ args = sys.argv
 # verbose flag
 verbose = '-v' in args
 
-target = os.path.realpath(os.path.dirname(__file__) + '/../requirements.txt')
+requirements = [
+    'PyMySQL'
+]
 
-with open(target, 'r') as file:
-    requirements = file.read().rstrip().split("\n")
-    requirements.reverse()  # reverse so the most important ones show first
-    try:
-        pkg_resources.require(requirements)
-    except DistributionNotFound as req:
-        if verbose:
-            print(req)
-        exit(1)
-    except VersionConflict as req:
-        if verbose:
-            print(req)
-        exit(2)
-    exit(0)
-
-exit(3)
+try:
+    pkg_resources.require(requirements)
+except DistributionNotFound as req:
+    if verbose:
+        print(req)
+    exit(1)
+except VersionConflict as req:
+    if verbose:
+        print(req)
+    exit(2)
+exit(0)