all: Remove Python 2.7 support.

Python 2.7 has been EOL since January 2020.

Ubuntu oldoldlts (Focal Fossa, 20.04) has Python 3.8.  Debian oldoldstable
(Buster, from 2019) has Python 3.7.  RHEL 8 (from 2019) has Python 3.6.

It's easier than ever to install a modern Python using uv.

Given this, it seems like a fine idea to drop Python 2.7 support.

Even though the build is not tested on Python as old as 3.3, I left
comments stating that "3.3+" is the baseline Python version.  However, it
might make sense to bump this to e.g., 3.10, the oldest Python 3 version
used during CI. Or, using uv or another method actually test on the oldest
Python interpreter that is desirable to support (uv goes back to Python 3.7
easily; in October 2025, the oldest supported Python interpreter version
will be 3.10)

Signed-off-by: Jeff Epler <jepler@gmail.com>

ports/stm32/boards/pllvalues.py

@@ -105,7 +105,7 @@ def compute_pll2(hse, sys, relax_pll48):
         # VCO_OUT must be between 192MHz and 432MHz
         if sys * P not in mcu.range_vco_out:
             continue
-        NbyM = float(sys * P) / hse  # float for Python 2
+        NbyM = sys * P / hse
         # scan M
         M_min = mcu.range_n[0] // int(round(NbyM))  # starting value
         while mcu.range_vco_in[-1] * M_min < hse:
@@ -121,7 +121,7 @@ def compute_pll2(hse, sys, relax_pll48):
             # N is restricted
             if N not in mcu.range_n:
                 continue
-            Q = float(sys * P) / 48  # float for Python 2
+            Q = sys * P / 48
             # Q must be an integer in a set range
             if close_int(Q) and round(Q) in mcu.range_q:
                 # found valid values
@@ -142,7 +142,6 @@ def compute_pll2(hse, sys, relax_pll48):
 
 
 def compute_derived(hse, pll):
-    hse = float(hse)  # float for Python 2
     M, N, P, Q = pll
     vco_in = hse / M
     vco_out = hse * N / M