Tests: Remove redundant Python version tests (#1075)

There were previously 6 virtually identical tests checking the handling of
a non-existent Python version being specified in `runtime.txt`. 

Only one is necessary - removing the rest will improve CI run time.

Closes @W-8110383@.

[skip changelog]

test/fixtures/python2_fail/requirements.txt

@@ -1 +0,0 @@
-requests

test/fixtures/python2_fail/runtime.txt

@@ -1 +0,0 @@
-python-2.7.99

test/fixtures/python3_4_fail/requirements.txt

@@ -1 +0,0 @@
-flask

test/fixtures/python3_4_fail/runtime.txt

@@ -1 +0,0 @@
-python-3.4.99

test/fixtures/python3_5_fail/requirements.txt

@@ -1 +0,0 @@
-flask

test/fixtures/python3_5_fail/runtime.txt

@@ -1 +0,0 @@
-python-3.5.99

test/fixtures/python3_6_fail/requirements.txt

@@ -1 +0,0 @@
-flask

test/fixtures/python3_6_fail/runtime.txt

@@ -1 +0,0 @@
-python-3.6.99

test/fixtures/python3_7_fail/requirements.txt

@@ -1 +0,0 @@
-flask

test/fixtures/python3_7_fail/runtime.txt

@@ -1 +0,0 @@
-python-3.7.99

test/fixtures/python3_8_fail/requirements.txt

@@ -1 +0,0 @@
-flask

test/run-versions

@@ -35,12 +35,6 @@ testPython2_warn() {
     assertCapturedSuccess
 }
 
-testPython2_fail() {
-    compile "python2_fail"
-    assertCaptured "Aborting"
-    assertCapturedError
-}
-
 testPython3_4() {
   compile "python3_4"
   assertCaptured $LATEST_34
@@ -56,12 +50,6 @@ testPython3_4_warn() {
   assertCapturedSuccess
 }
 
-testPython3_4_fail() {
-    compile "python3_4_fail"
-    assertCaptured "Aborting"
-    assertCapturedError
-}
-
 testPython3_5() {
   compile "python3_5"
   assertCaptured $LATEST_35
@@ -78,12 +66,6 @@ testPython3_5_warn() {
   assertCapturedSuccess
 }
 
-testPython3_5_fail() {
-    compile "python3_5_fail"
-    assertCaptured "Aborting"
-    assertCapturedError
-}
-
 testPython3_6() {
   updateVersion "python3_6" $LATEST_36
   compile "python3_6"
@@ -102,12 +84,6 @@ testPython3_6_warn() {
   assertCapturedSuccess
 }
 
-testPython3_6_fail() {
-    compile "python3_6_fail"
-    assertCaptured "Aborting"
-    assertCapturedError
-}
-
 testPython3_7() {
   updateVersion "python3_7" $LATEST_37
   compile "python3_7"
@@ -134,12 +110,6 @@ testPython3_7_warn() {
   fi
 }
 
-testPython3_7_fail() {
-  compile "python3_7_fail"
-  assertCaptured "Aborting"
-  assertCapturedError
-}
-
 testPython3_8() {
   updateVersion "python3_8" $LATEST_38
   compile "python3_8"
@@ -166,8 +136,9 @@ testPython3_8_warn() {
   fi
 }
 
-testPython3_8_fail() {
-  compile "python3_8_fail"
+testPythonVersionInvalid() {
+  compile "python_version_invalid"
+  assertCaptured "Requested runtime (python-3.8.99) is not available for this stack"
   assertCaptured "Aborting"
   assertCapturedError
 }