docs: Replace ufoo with foo in all docs.

Anywhere a module is mentioned, use its "non-u" name for consistency.

The "import module" vs "import umodule" is something of a FAQ, and this
commit intends to help clear that up.  As a first approximation MicroPython
is Python, and so imports should work the same as Python and use the same
name, to a first approximation.  The u-version of a module is a detail that
can be learned later on, when the user wants to understand more and have
finer control over importing.

Existing Python code should just work, as much as it is possible to do that
within the constraints of embedded systems, and the MicroPython
documentation should match the idiomatic way to write Python code.

With universal weak links for modules (via MICROPY_MODULE_WEAK_LINKS) users
can consistently use "import foo" across all ports (with the exception of
the minimal ports).  And the ability to override/extend via "foo.py"
continues to work well.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

docs/esp32/quickref.rst

@@ -98,7 +98,7 @@ A useful function for connecting to your local WiFi network is::
                 pass
         print('network config:', wlan.ifconfig())
 
-Once the network is established the :mod:`socket <usocket>` module can be used
+Once the network is established the :mod:`socket <socket>` module can be used
 to create and use TCP/UDP sockets as usual, and the ``urequests`` module for
 convenient HTTP requests.
 
@@ -113,7 +113,7 @@ to reconnect forever).
 Delay and timing
 ----------------
 
-Use the :mod:`time <utime>` module::
+Use the :mod:`time <time>` module::
 
     import time
 
@@ -459,15 +459,15 @@ SD card
 
 See :ref:`machine.SDCard <machine.SDCard>`. ::
 
-    import machine, uos
+    import machine, os
 
     # Slot 2 uses pins sck=18, cs=5, miso=19, mosi=23
     sd = machine.SDCard(slot=2)
-    uos.mount(sd, "/sd")  # mount
+    os.mount(sd, "/sd")  # mount
 
-    uos.listdir('/sd')    # list directory contents
+    os.listdir('/sd')    # list directory contents
 
-    uos.umount('/sd')     # eject
+    os.umount('/sd')     # eject
 
 RMT
 ---