Remove deprecated `using` qubit allocation syntax (#777)

tutorials/ExploringGroversAlgorithm/ExploringGroversAlgorithmTutorial.ipynb

@@ -341,7 +341,7 @@
    "source": [
     "<details>\n",
     "    <summary><b>Click here for the complete answer validation code</b></summary>\n",
-    "<code>    using (y = Qubit()) {\n",
+    "<code>    use y = Qubit() {\n",
     "        oracle(register, y);\n",
     "        if (MResetZ(y) == One) {\n",
     "            Message(\"Correct!\");\n",
@@ -437,7 +437,7 @@
     "    GroversAlgorithm_Loop(register, oracle, iterationCount);\n",
     "    set finalAnswer = ResultArrayAsBoolArray(MultiM(register));\n",
     "    Message($\"Verifying answer {finalAnswer}\");\n",
-    "    using (y = Qubit()) {\n",
+    "    use y = Qubit() {\n",
     "        oracle(register, y);\n",
     "        if (MResetZ(y) == One) {\n",
     "            set isAnswerCorrect = true;\n",
@@ -550,7 +550,7 @@
     "for (i in 1 .. 100) {\n",
     "    GroversAlgorithm_Loop(register, oracle, iterationCount);\n",
     "    let answer = ResultArrayAsBoolArray(MultiM(register));\n",
-    "    using (y = Qubit()) {\n",
+    "    use y = Qubit() {\n",
     "        oracle(register, y);\n",
     "        if (MResetZ(y) == One) {\n",
     "            set successCount += 1;\n",

tutorials/Qubit/Qubit.ipynb

@@ -160,14 +160,14 @@
     "// The qubit is deallocated once it's not used any longer\n",
     "```\n",
     "\n",
-    "> Before Q# 0.15 the syntax for qubit allocation was different:\n",
+    "> An alternative syntax for qubit allocation defines the scope in which the allocated qubits are available explicitly:\n",
     "```c#\n",
     "// This statement allocates a qubit, and binds it to the variable q\n",
-    "using (q = Qubit()) {\n",
+    "use q = Qubit() {\n",
     "    // You can work with the qubit here\n",
     "    // ...\n",
     "}\n",
-    "// The qubit is no longer allocated outside of the 'using' block\n",
+    "// The qubit is no longer allocated outside of the 'use' block\n",
     "```\n",
     "\n",
     "Freshly allocated qubits start out in state $|0\\rangle$, and have to be returned to that state by the time they are released. If you attempt to release a qubit in any state other than $|0\\rangle$, your program will throw a `ReleasedQubitsAreNotInZeroStateException`. We will see why it is important later, when we look at multi-qubit systems."